MULTI-PURPOSE AIRCRAFT

Abstract: Several innovative systems for an aircraft, and aircraft incorporating them, are disclosed. Features include inboard-mounted engine(s) (24, 25) with a belt drive system (84, 99) for turning wing-situated propellers (8, 9); compound landing gear integrating ski (29, 114), pontoon and wheel (18, 19, 21) subcomponents; pivotal mounting armatures (6, 7) for landing gear and/or propellers which provide a plurality of possible landing gear and/or propeller configurations; and a compound wing structure (14, 15) featuring extendable wing panels (4, 5) that permit the wing span of the aircraft to be nearly doubled while in flight. Aircraft incorporating such features will enjoy several safety advantages over conventional multi-engine aircraft and will be capable of modifications during flight which permit landings on any of snow, hard surfaces (runways) and water.

Description: MULTI-PURPOSE AIRCRAFT Technical Field The present invention relates to general aviation aircraft. More particularly, the present invention relates to a novel aircraft adaptable to recreational, utility, or business uses and distinguished by design features permitting fuselage expansion and in-flight alteration of its configuration. Background Art Many different types of aircraft have been designed to meet, within the limits of airworthiness, the particular requirements of fliers. Thus, aircraft designs and design modifications are well known which will permit aircraft to land on different surfaces, such as ski-type landing gear for landings on snow, hull-type fuselage and pontoons for amphibious landings, and wing designs having increased wing surface areas and shapes for takeoff and landing in short distances. Some features have also been developed that permit modification of an aircraft's configuration (and thus its flight characteristics) while in flight. For example, some jet fighter aircraft are often equipped with wing panels that are rotated out from the fuselage to increase wing span and lower stall speed for takeoffs and landings but are swept back during flight to increase maneuverability and decrease drag and bending stresses. Although the adaptability of an aircraft to different uses and to different flight and landing conditions is always desirable, most design modifications that suit an aircraft to a particular specialized use necessitate design compromises that adversely affect the aircraft's performance in some other aspect. For instance, amphibious aircraft designs have been limited by the necessity of placing the engine high over the wing, to avoid interference with the propeller by the spray of water from takeoff or landing. This is a design compromise that creates a high thrust line for the aircraft and also additional drag. Also, the design sophistication and structural requirements necessary to adopt such capabilities as "swing" wings are impractical and expensive for private recreational aircraft. Accordingly, there is a continuing need for the development of aircraft that are suited to a variety of uses and which can satisfy the requirements and demands of a wide variety of commercial and recreational fliers. Disclosure of the Invention It is an object of the present invention, therefore, to provide a novel twin-engine propeller-driven aircraft (although many features of this invention will be applicable to jet- powered aircraft and to aircraft having any number of engines). It is a further object of the present invention to provide a basic aircraft design that can be adapted to serve a wide variety of specialized uses without entailing modification of the design or extensive refitting. It is a further object of the present invention to provide a basic aircraft design capable of a wide range of uses but without introducing design compromises that limit or reduce specific flight performance characteristics. It is a further object of the present invention to provide an aircraft capable of landing on snow, water or land without pre-flight modification of the landing gear. It is a further object of the present invention to provide a short takeoff and landing (STOL) aircraft having a high degree of maneuverability and capable of trimming drag and decreasing wing surface area and wing span in flight. It is a further object of the present invention to provide a basic design for an aircraft that is expandable from 2 seats to 8 or more seats without entailing redesign of the airfoil or fuselage. It is a further object of the present invention to provide a basic design for an aircraft that is convertible from a passenger-carrying configuration to a cargo-carrying configuration (or to other specialized cabin configurations) without entailing redesign of the airfoil or fuselage. It is a further object of the present invention to provide a novel landing gear design integrating skis, wheels, and pontoons, which can be converted to the appropriate configuration during flight. It is a further object of the present invention to provide a propeller-driven, multi-engine aircraft with improved safety characteristics. In particular, it is an object of the invention to provide aircraft of unprecedented safety through an aircraft design which eliminates many of the leading causes of aviation accidents, including asymmetrical thrust conditions due to an engine failure, propeller blade separation (i.e., loss of a propeller due to damage to the propeller blades and the resulting vibration and breakage), rapid power loss (engine failure) during takeoff or climbout, inappropriate configuration or selection of landing gear, and accidents related to the position of the propeller on an aircraft on the ground (e.g., unintentional contacts with ground objects or people). It is a further object of the present invention to provide a novel propeller drive system for a propeller-driven aircraft and to provide an aircraft design characterized by unifying mounting structures for the propellers and landing gear, allowing adjustment of propeller position relative to the airfoil as a function of landing configuration of the aircraft. It is a further object of the present invention to provide a 2-8 seat aircraft that is easy to service and maintain and which maintains airworthiness in a variety of emergency situations. These and other objects are accomplished herein by a novel type of aircraft and novel components thereof having a number of innovative design features including: telescoping wing extensions; integrated multiple landing gear mounts permitting skis, wheels, or pontoon outriggers to be rotated into landing position, at the option of the pilot; modular fuselage sections permitting the addition of seats or cargo area without requiring redesign or refitting of wing or tail components; propellers mounted on their own shafts which are belt-driven from inboard engines; a primary structure permitting support of the engine mass by the ftiselage structures rather than the wings and permitting large fuselage openings for easy engine access, efficient cargo handling, enhanced pilot visibility, or enhanced passenger comfort. Utilization of one or more of these features provides an aircraft of improved safety, performance, reliability, efficiency, and versatility over aircraft currently available. Brief Description of the Drawings Figure 1 is a perspective view of an aircraft according to the present invention, showing telescoping wing sections and landing gear fully extended. The aircraft is shown in a configuration advantageous for takeoff and landing on a hard surface. Figure 2 is a perspective view of an aircraft according to the present invention as illustrated in Figure 1 but with an alternative, conventional tail design (as opposed to the "T" tail shown in Figure 1). Figure 3 is a perspective view of an aircraft according to the present invention, with the propeller mounts and landing gear retracted. The aircraft is shown shortly after takeoff or in a configuration suitable for low-speed flight. Figure 4 is a perspective view of an aircraft according to this invention as depicted in Figure 3, showing telescoping wing sections in a fully retracted position. Figure 5 is a perspective view of an aircraft according to this invention as depicted in Figure 4, except that a modular fuselage section has been removed to attain a shorter fuselage. Figure 6 is a front elevation view of an aircraft according to the invention, shown in the hard surface takeoff and landing configuration similar to Figure 1. Figure 7 is a front elevation view of the aircraft as illustrated in Figure 6, but with telescoping wing panels in a fully retracted position. Figure 8 is a front elevation view of an aircraft according to the invention, shown in the configuration appropriate for takeoff or landing on snow or ice. Figure 9 is a front elevation view of an aircraft according to the invention, shown in a configuration appropriate for takeor- . * >r landing on water. Figure 10 is a front elevation view of an aircraft as depicted in Figure 9, in a configuration appropriate for slow speed water taxiing operation. Figure 11 is a front elevation view of an aircraft according to the invention, shown in a high speed cruise configuration. This is the same configuration as depicted in Figures 4 and 5. Figure 12 is a front elevation view of an aircraft as depicted in Figure 11, shown in a low speed configuration, with telescoping wing sections fully extended. This is the same overall configuration for the aircraft as illustrated in Figure 4. Figure 13 is a plan view of an aircraft as depicted in Figures 3 and 12. Figure 14 is a plan view of an aircraft as depicted in Figures 1, 6, and 8. Figure 15 is a plan view of an aircraft as depicted in Figures 4 and 11. Figure 16 is a perspective view of the starboard wing extension assembly of a compound wing structure according to the present invention. This figure shows the internal supporting beam structures of the extendable wing section. Figure 17 is a detail of the encircled portion XVII of Figure 16, showing the inboard end of the supporting spars of the extendable wing section. Figure 18 is a perspective view of the starboard wing extension assembly as depicted in Figure 16, showing its position relative to the main wing section (shown in phantom lines) when the wing extension panel is fully extended (ref. Figure 13). This figure also shows the positioning of roller assemblies enabling rolling extension of the wing extension panels and shows the relative position of the support structures of a port wing extension assembly. Figure 19 is a detail of the encircled portion XIX of Figure 18, showing the positioning of rollers in relation to the supporting spars for the extendable wing section. Figure 20 is a perspective view of the starboard wing extension assembly as depicted in Figure 16, showing its position relative to the main wing section (shown in phantom lines) when the extension panel is fully retracted (ref. Figure 15). Figures 21, 22, and 23 show front cross-sectional views of the starboard wing lift spars and supporting rollers in fully extended (Figure 21), intermediate (Figure 22), and fully retracted (Figure 23) configurations. Figure 24 is a cross-sectional view of a wing extension panel taken on the line A-A in Figure 13. Figure 25 shows a cross-sectional view of a wing taken on the line B-B in Figure 13. Figure 26 shows a cross-sectional view of a wing on the line C-C in Figure 15. Figure 27 is a perspective view of the supporting lift and drag spars of a starboard wing extension assembly according to the invention, showing the interlocking relationship of lift and drag spars of a port wing extension assembly and also showing a preferred cable mechanism useful for extending and retracting the extendable wing sections. The arrows indicate direction of motion during wing retraction. Figure 28 is an enlarged detail of encircled portion XXVIII of Figure 27. Figure 29 is a perspective view of starboard wing support structures similar to Figure 27, showing an alternative screw-type mechanism for extending and retracting the wing extension panels. Figures 30 and 31 are cross-sectional views of a wing taken on line J-J of Figure 15, showing a preferred mechanism for coordinated actuation of the ailerons on the fixed wing section and on the wing extension panel. The components of Figures 30 and 31 are exactly the same; the two figures show simultaneous adjustment of the positions of the fixed wing aileron (10) and the extension panel aileron (12) relative to the stationary surface of the wing (2) as the ailerons are trimmed from a raised position (Figure 30) to a lowered position (Figure 31). Figure 32 shows the preferred design for actuation of the ailerons using a cable system for the extension ailerons (12) and a push-pull rod system for the fixed wing section flap (72) and aileron (10). Figure 33 is a perspective diagrammatic view of an alternate design for the actuation of the aileron systems of an aircraft according to the invention. In contrast to the actuation system depicted in Figure 30, this figure shows a cable system for actuating both the flaps (72) and ailerons (10) of the fixed wing section and the ailerons (12) of the wing extension assembly. Figure 34 is a cross-sectional view of the fuselage taken on line I-I in Figure 15, showing the relative positions of the powerplants and the belt drive system in a preferred embodiment of this invention. Air cooled aircraft engines are depicted. Figure 35 is a cross-sectional front elevation of an aircraft according to the invention showing the positioning of the engines in the fuselage, the belt and pulley system for driving the propellers, and the pivotally mounted armatures providing pivoting mounts for both the landing gear and the propellers. The components depicted in this figure are shown in a configuration typical of in-flight operation (cf. Figure 4), with landing gear retracted into the fuselage. Figure 36 is a schematic plan view looking down on a compound wing structure according to the invention and a preferred belt drive system for turning pusher-type propellers mounted in pivoting armature mounts according to the invention. The drawing shows the relative positions of the port wing extension panel (5) and the starboard wing extension panel (4) inside the fixed wing section (1). Also visible in this schematic view are structural components of the wing extension panels, i.e., front (31) and rear (33) lift spars of the port wing extension assembly and port drag spar (35) (diagonal lines), as well as the starboard front (30) and rear (32) lift spars and drag spar (34) (cross-hatched) of the starboard wing extension assembly. The wing extension panels are shown partly extended, and the interlocking juxtaposition of the supporting spars (30, 31, 32, 33, 34, 35) within the fixed wing structure (1) is also shown. Also illustrated in Figure 36 is a preferred arrangement of port (diagonal lines) and starboard (cross-hatched) drive belts (84, 99) for actuating port and starboard propellers (9 and 8, respectively) via propeller drive shafts (81). Figure 37 is a side elevation of the engines and drive belt system disclosed herein, showing details of the gear box (110) of Figure 34. Figure 38 is a perspective view of starboard and port curved mounting armatures and mounted propellers, shown in isolation from the aircraft (cf. Figure 4) but in proper relation to each other. The armatures are shown in the relative positions they would have, e.g., in an aircraft as depicted in Figure 4, wherein the propeller centers are in line with the planes of the wings and the landing gear are fully retracted inside the fuselage. Figure 39 is a frontal diagram of two pivotal mounting armatures in the same relation as depicted in Figure 38, provided to indicate the preferred shape and dimensions of such armatures. Figure 40 shows a cross-sectional view of a wing taken on the line D-D of Figure 15. Figure 41 is a perspective view of starboard and port curved mounting armatures and mounted propellers, shown in isolation from the aircraft (cf. Figure 8, Figure 57) but in proper relation to each other. The armatures are shown in their relative positions, e.g., in an aircraft as depicted in Figure 1 , wherein the propellers are positioned above the surface of wings and caster-type wheel gear are deployed, as appropriate for a runway landing. Figure 42 is a perspective view of starboard and port curved mounting armatures and mounted propellers, shown in isolation from the aircraft (cf. Figure 9) but in proper relation to each other. The armatures are shown in their relative positions, e.g., in an aircraft as depicted in Figure 9, wherein the propellers are raised to their maximum distance above the wings and the pontoon gear are fully deployed, as appropriate for a water landing. Figure 43 is a cross-sectional view of a wing taken on the line E-E of Figure 14, showing the relative position of the propeller mounting to the wing when the aircraft is in a takeoff/landing configuration as depicted in Figures 1, 6, and 8. In a cutaway, the relationship between the propeller, propeller shaft and propeller drive belt is shown. Figure 44 is a cross-sectional diagrammatic view of the forward fuselage of an aircraft of the invention, taken on line F-F in Figure 11, showing the structures of a forward landing gear component of the compound landing gear in a fully retracted configuration. Figure 45 is a similar forward cross-sectional view to Figure 44, except that the forward landing gear are shown partially extended. Figure 46 is a similar cross-sectional view to Figure 44, except the forward landing gear are shown fully extended (uncompressed), in a configuration typical of the instant before landing or the instant after takeoff. Figure 47 is a similar cross-sectional view to Figure 44, except that the forward landing gear are shown extended and fully compressed, in a configuration typical of a high-impact landing on a hard surface. Figure 48 is a similar forward cross-sectional view to Figure 44, except that the forward landing gear are shown fully extended to support the weight of the nose of the aircraft and in a configuration appropriate to taxiing. Figure 49 is a similar cross-sectional view to Figure 44, except that the skis of the compound forward landing gear are shown fully extended, in a configuration appropriate to landing on a snowy or icy surface. Figure 50 is a cross-sectional diagrammatic view of the central portion of the fuselage of an aircraft according to the invention, taken on line F-F of Figure 11. The outer fuselage panels that enclose the main central landing gear component of a compound landing gear are shown in the proper in-flight position, forming an aerodynamically smooth outer surface. Figure 51 is a cross-sectional view similar to Figure 50, except the outer fuselage panels are shown by phantom lines in order to expose the structures of the main central landing gear. The components of a preferred main central landing gear according to the invention are shown, fully folded and enclosed within the fuselage, i.e., in their fully retracted and stowed position appropriate during flight. The relative positions of the inboard engines (shown in silhouette) and belt drive mechanisms, landing gear, primary fuselage structure, wing structures, and wing extension assemblies are shown in this figure. Figure 52 is a perspective elevation of a preferred main central landing gear assembly, shown in a fully retracted configuration, as the assembly would be positioned in flight. In such configuration, the lower surface of the skis would form part of the outer surface of the aircraft's fuselage; the rest of the landing gear assembly would be inside the fuselage of the aircraft, out of the airstream. Figure 53 is a perspective elevation of a preferred main central landing gear component of the compound landing gear of the invention. The assembly shown unifies central wheel-type landing gear (not visible in this view), ski-type landing gear and flotation-assisting hollow design ski struts. The assembly is shown in a deployed configuration that places the wheel-type landing gear in a vertical position suitable for use in landing on a hard surface or runway. (Cf. Figure 54.) In this position the skis are semi-deployed and will not meet the surface during a normal landing. Figure 54 is a cross-sectional view of the midsection of the fuselage of an aircraft according to the invention, taken on line P-P of Figure 7 and depicting the compound landing gear deployed so as to make use of the wheeled gear, i.e., in the configuration most suitable for landing on, taking off from, and taxiing on a hard surface. Figure 55 is a cross-sectional view of the midsection of the fuselage of an aircraft according to the invention, illustrating compound landing gear deployed so as to make use of the main ski landing gear, i.e., in the configuration most suitable for landing on, taking off from, and taxiing on a snow-covered surface. Figure 56 is a cross-sectional front elevation of the midsection of the aircraft as illustrated in Figure 54, showing structures of the main central and stabilizing landing gear components in the configuration appropriate to takeoff and landing or taxiing on hard surface runways. (Cf. Figure 7.) Several structural elements not related to the landing gear are omitted from this view. Figure 57 is a cross-sectional front elevation of the midsection of the aircraft similar to the configuration depicted in Figure 56, except that the deployment of the landing gear has been modified as appropriate for takeoff and landing on intermittent snow over a hard surface runway. Several structural elements not related to landing gear are omitted from this view. Figure 58 is a cross-sectional front elevation of the midsection of the aircraft as illustrated in Figure 56, showing structures of the main central landing gear and stabilizing landing gear components in the configuration appropriate for takeoff and landing on snow. (Cf. Figure 8.) Several structural elements not related to landing gear are omitted from this view. Figure 59 is a cross-sectional front elevation of the midsection of the aircraft similar to the configuration depicted in Figure 56, with main central landing gear retracted, showing the mounting armatures (6 and 7), and thus the pontoon subcomponents (22 and 23) fully deployed, i.e., in the configuration appropriate to takeoff and landing on water. (Cf. Figure 9.) Several structural elements not related to landing gear are omitted from this view. Figures 60 and 61 show schematic illustrations of steering mechanisms for aircraft of this invention. Figure 60 shows a preferred steering control system, in which control of the front and rear wheels are linked such that turning the rear (main) gear simultaneously turns the nose landing gear. Figure 61 illustrates a similar steering control system in which the nose and main gear are controlled independently. Figure 62 is an exploded perspective view of an aircraft according to the invention showing the modular components of the fuselage and major components of the aircraft. Alternative wide-fuselage cargo-type components (231 and 232) to the standard passenger-type upper fuselage components (3 and 2) are also shown. Figure 63 shows a plan view of a wide-fuselage embodiment of the invention. This fuselage option can be compared to the standard fuselage configuration shown in Figure 15. Best Mode for Carrying Out the Invention Preferred embodiments of the present invention will be described below with reference to the drawings. It will be immediately appreciated, however, that the design features described may be altered or modified for particular purposes and that the production of many alternative embodiments of the aircraft described herein will be possible in view of this disclosure. All such alterations, modifications and additional embodiments are contemplated herein and are intended to fall within the scope of this description and the appended claims. The following description is not intended to limit the scope of the invention in any way. Preferred embodiments of a Complete aircraft according to the present invention are shown in various configurations and views in Figures 1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15 and 62. The preferred features of the aircraft include compound wings comprising a fixed wing section also housing port and starboard extendable wing panels, which can be deployed (in-flight, if desired) to increase wing surface area and lift; pivoting mounting armatures that serve as propeller mounts and also as aft landing gear mounts, the armatures serving to change simultaneously the position of the propellers and the compound landing gear with respect to the rest of the aircraft, i.e., placing the propellers in the optimal position for landing on or taking off from a variety of surfaces or for cruising flight, such positioning of the propellers occurring automatically as compound landing gear mounted on the armatures are rotated to expose the appropriate type of landing gear (wheeled gear, skis, pontoons) for different landing surfaces (tarmac, snow, water) or are rotated to nest in recesses in the fuselage of the aircraft during flight; modular fuselage design permitting augmentation of the aircraft in production to meet different passenger-carrying or cargo-carrying needs without re-design; elimination of an aft fuselage section and a stronger, more easily fabricated tail section; and a power train featuring inboard engine mounting (preferably twin, tandemly mounted and opposed engines) and a novel belt drive for propellers. Referring to Figure 1. an aircraft according to the invention and featuring several design innovations is illustrated. The overall configuration of this embodiment is of a cantilever high- wing, amphibious monoplane, preferably having a hull-bottomed fuselage and twin rear-facing, pusher-type propellers. The wings are compound in structure, comprising a main wing section (1) fixed to the main fuselage structure (300), port and starboard leading edge slats (15 and 14, respectively), and port and starboard main ailerons (11 and 10, respectively). The main fuselage section includes an aft tail section (310), shown in Figure 1 as a cantilever T tail, with steering surfaces including a rudder (311) and an elevator (312). The primary ailerons 10 and 11 of the fixed main wing section (1) are aerodynamically shaped surfaces on the trailing edges of the wing section and are used for control of the aircraft motion around the longitudinal axis (roll control), primarily at high speeds. The main wing section (1) also houses two telescoping extendable wing sections (4 and 5), which can be extended (pictured) or fully retracted within the main wing section (1), as illustrated in Figures 4, 11 and 20. The extendable wing sections (port, 5; starboard, 4) also have leading edge slats (port, 17; starboard, 16) and ailerons (port, 13; starboard, 12), as on the main wing section (1). The leading edge slats (14 and 15) of the fixed wing section (1) are (preferably) forwardly extendable to change the lift characteristics of the compound wing, and the ailerons (10-13) are trimmed to steer the aircraft in flight. Preferably the port main wing aileron (11) and the port extension panel aileron (13) are actuated by the same or connected mechanisms, and the starboard main wing section aileron (10) and die starboard extension panel aileron (12) are similarly co-actuated, so that the movements of both sets of ailerons are completely coordinated and may be effected without using multiple controls. Likewise, it is preferred that the leading edge slats (14 and 15) are co-actuated, so that their operation is coordinated and requires manipulation of a minimum number of controls. In most preferred embodiments, the compound main wing section (1) further includes recesses for accepting pivoting propeller mounts (6, 7), which may be rotated to raise the propellers above the level of the wing (preferable for water landings) or to nest the propeller mounts in recesses in the wing (see, Figures 3-5) to bring the propellers even with the wing surface (preferable for climbout and cruising flight). The compound wing structure described herein lends several advantages to an aircraft. When the extendable wing panels (4, 5) are fully retracted and thus completely housed within the fixed main wing section (1), out of the airstream, the wing span of the aircraft is considerably shortened (e.g., reduced almost 50%), giving the aircraft increased maneuverability and higher cross-wind stability. The ability to retract the wing panels (4, 5) and thereby significantly reduce the wing span leads to improved safety characteristics for the aircraft in that the wing bending stresses in the cruise and maneuvering configurations (see, Figures 4 and 5) are reduced. Wing stresses are also reduced by the interlocking juxtaposition of the supporting spars (discussed, infra: ref. Figure 36) of the extendable wing sections, when the wing sections are fully retracted. The interlocking support spar design also makes it possible to increase the wing span up to 90-95% while maintaining the structural integrity and operability of the wing, a capability that was not attainable with previous designs. The ability to extend the extendable wing sections (4, 5) while in flight makes aircraft according to the present invention ideal for pilot training by providing the capability of simulating the flying characteristics of a wide variety of aircraft. When the extension panels are retracted, the aircraft has speed, maneuverability and wing stress-bearing characteristics similar to aerobatic or military combat aircraft; when the wing extension panels are fully extended, the aircraft simulates the lower stall speed, greater lift and high altitude flying characteristics of STOL, commuter and patrol aircraft; and with intermediate, variable extension of the telescoping wing extension panels, flight characteristics can be varied to match those of other types of aircraft or to tailor the aircraft's properties in-flight to meet changing air and wind conditions, or to prepare for landing on or takeoff from a variety of different surfaces. The retractable wing section feature also makes the aircraft of this design suitable for full-scale aerodynamic testing of new airfoil shapes in-flight. For example, new airfoil designs may be fitted to the aircraft as extendable wing sections (4, 5), gradually and safely extended while the aircraft is in flight, and retracted out of the airstream if undesirable characteristics are detected. Additional advantages provided by the telescoping wing features include improved safety in conditions of ice accumulation on the wings by virtue of the ability to retract a major portion of the wing during ice accumulation and extend said wing sections (free of ice) during landing. The aircraft may also convert from a relatively long wing span that is advantageous for takeoff and landing, fuel efficient long range flight, and high altitude flight to a shorter wing span that is efficient for high speed flight and advantageous for storage and operation around obstacles (such as other aircraft) on the ground or in underdeck storage on a ship. This wing design also provides high wing loading (weight per wing area) during cruise (retracted wing panels), which gives pilot and passengers a relatively smooth ride through turbulent air, and a low wing loading (extended wing panels) during takeoff and landing to provide an improved operational safety margin at low airspeeds (greater lift, lower stall speeds) and lower landing speeds, resulting in a reduced potential for damage or injury in landing accidents. This wing design also provides a means of expanding wing surface area for carrying larger payloads or a larger quantity of fuel for long trips, or a means of reducing wing surface area for more efficient cruising flight with minimum payloads or low fuel. Referring again to Figure 1, the fixed main wing section (1) and an optional fuselage extension module and cabin extension assembly (2) are fixedly attached to the main fuselage section (300). An upper cockpit assembly (3), attached to a forward cabin module (233 in Figure 62) that houses the forward landing gear (e.g., 21 and 29), is attached end-to-end to an upper cabin extension assembly (2) and a cabin extension module (234 in Figure 62), to provide a continuous enclosed cockpit and cabin area forward of the main fuselage section (300). Alternatively, as pictured in Figure 5, the forward cabin module and the upper cockpit assembly (3) may be attached end-to-end to the main fuselage section (300), e.g., where no additional cabin/cargo space or a smaller, lighter weight aircraft is desired. The nose assembly (3), any fuselage extensions (2), and the main fuselage section (300) together comprise the fuselage and tail of the aircraft as a whole. The front landing gear are comprised of elements such as the front wheel (21) and d e front skis (29) and may be mounted in and attached to the forward section of the fuselage through support and extension/retraction members explained in more detail infra. The wing extension panels (4 and 5) are mounted inside the fixed wing section (1) so as to be simultaneously extendable laterally out from the starboard and port wing tips (38 and 39, respectively) or simultaneously retractable into the fixed wing section (1). When fully retracted, the extension panels (4 and 5) are completely enclosed within die fixed wing section (1) of the aircraft, and the extension panel wing tips (36 and 37) meet and preferably nest into the fixed wing tips (38 and 39) to form an aerodynamic teardrop wing tip. (See, e.g., Figures 4 and 7.) The embodiment of Figure 1 also shows curved mounting armatures (6 and 7) which are pivotally attached to the rear of the fixed wing section (1), near the fuselage. The armatures (6 and 7) not only provide a mount for the propellers (8 and 9) but also provide a mount for rear stabilizer landing wheels (19 and 20) and flotational pontoon assemblies (22 (not visible in this figure) and 23), which serve as outrigger-like stabilizers during amphibious operations. The mounting armatures (6 and 7) are generally pan-shaped when viewed edge-on (see, e.g., Figure 5 and other front elevations), and the curvature of the armatures permits the pilot to bring the wheeled landing gear (19 and 20) or alternatively the pontoon landing gear (22 and 23) into position for use by causing the armatures to rotate about their pivotal attachment. Additionally, because the armatures (6 and 7) also serve as a mount for the propellers (8 and 9), rotating the desired landing gear (wheels or pontoons) into position for use simultaneously will change the positions of the propellers relative to the wing and fuselage. The armatures are shaped so that at the maximum rotation of the lower end of each armature away from the fuselage of the aircraft, that is, to expose the pontoon landing gear (22 and 23), the propellers simultaneously are rotated away from and above the wing, toward die centerline of the aircraft, so that the propellers are raised to a maximum height above the water and are shielded from water spray by the wings and fuselage. (See, Figure 9.) The mounting armatures (6 and 7) are preferably designed so that the entire propeller can be raised above the surface of the wing when a water landing is attempted. Water spray damages propellers: water droplets can cause pitting of the propeller blades, the tips of which are moving at near-sonic speeds. In conventional amphibious aircraft designs, at least the lower arc of the propeller is often exposed to water spray, but in preferred embodiments of this invention, the mounting armatures will cause the entire arc of the propeller to be shielded from water spray by the wings, when the propellers are positioned for a water landing. For hard surface landings, also, the armatures (6 and 7) will position the propellers above the wing, where the propellers are much less likely to contact objects on the ground or to come into contact with people moving around the aircraft. In the most preferred embodiments, the armatures (6 and 7) are additionally shaped to nest in recesses of the wings directly above the flaps (72, actually split flaps, only a fraction of the thickness of the wing) and on either side of the fuselage (305), when the armatures are pivoted to align the propellers with the surface of the wing and to retract the landing gear. This means that below the pivot point, the outer surfaces of the armatures (6 and 7) when fully rotated will become flush with the surface of the main fuselage section (300); and above the pivot point, die outer surface of the armatures (6 and 7) when fully rotated will be flush with and become part of the aerodynamic surface of the fixed wing section (1). Recognizing that many modifications and alternative choices of design or materials are possible from the description herein, a most preferred embodiment contemplated for the present invention will have the general configuration depicted in Figure 1 with the following dimensions: center (fixed) wing section (1 in Fig. 1): NACA 66 3 -018 at root and tip, dihedral 3 degrees, sweep -3.28 degrees (forward) at the A chord, with two internally mounted telescoping wing extension panels, 0 degrees sweep; wing span (panels fully retracted): 26 feet (7.92 meters); wing span (panels fully extended): 50 feet (15.24 meters, 92.31 % increase over fully retracted); wing chord at fixed root: 10 feet, 8 inches (3.25 meters); wing chord at fixed tip: 6 feet, 8 inches (2.03 meters); wing chord at extension root: 3 feet, 8 inches (1.12 meters); wing chord at extension tip: 3 feet, 8 inches (1.12 meters); wing aspect ratio (retracted) 3.125; wing aspect ratio (extended) 8.33; moveable leading edge slats on center wing section, fixed leading edge slats on extension sections; construction: all wing sections preferably constructed of flush riveted aluminum; cantilever T-type tail constructed of flush riveted aluminum, having a horizontal stabilizer and an elevator (optionally including servo-tabs); tailplane span: 14 feet, 7 inches (4.44 meters); lower fuselage: riveted aluminum for amphibious hull and main fuselage section (300 in Fig. 1); upper fuselage (cabin): fiberglass composite; fuselage construction: 3 sections (nose, center cabin, and main fuselage (engine enclosure) including tail section) bolted end-to-end; overall length: 40 feet (12.19 meters); overall height: 12 feet, 4 inches (3.75 meters); wheelbase: 20 feet, 10 inches (6.35 meters); wheel track: 10 feet, 6 inches (3.2 meters); propeller diameter: 6 feet, 6 inches (1.98 meters). Of course, the foregoing dimensions and preferred materials may be modified without departing from the concept of this invention, so long as the inventive features, as recited in the claims, are incorporated. Referring to Figure 2, an aircraft of the same general configuration as illustrated in Figure 1 is shown, except that an alternative tail section in the shape of an inverted "T" is shown, equipped with a rudder (311) and a single elevator plane (312). All other features of this aircraft are as discussed above for Figure 1. Most preferred embodiments of die invention will have the T tail configuration of Figure 1, wherein the tail surfaces are in the direct prop wash when the propellers are raised above the wing and are out of the prop wash when the propellers are lowered to be level with the wing. This design lends maneuverability to the aircraft at landing and takeoff speeds, when maneuverability is most critical. Including various of the inventive features of this invention into an aircraft design permits incorporation of a unique tail configuration, which is apparent in the embodiments of Figures 1 and 2. Inboard mounting of the engines in the aft portion of the fuselage, under and just aft of the wings (ref. Figure 51) makes the inclusion of an fuselage section aft of the wings undesirable and impractical; therefore, the fuselage can advantageously begin to taper immediately aft of the wings to form a vertical tail section as shown. The tail section can taper in a straight line from the end of the fuselage, in contrast to conventional designs including an aft fuselage, which leads to structural advantages in that stiffening stringers and such members are not bent or made to follow contours and are thus able to withstand greater stresses. The horizontal stabilizer plane and elevator of the tail are supported by a much stronger and stiffer tail structure, and dius undesirable flutter of the tail control surfaces is eliminated. The illustrated vertical tail (Figure 1) is highly swept aft to balance aerodynamic forces, to reduce drag, to clear the propeller arcs at all propeller positions, etc., which leads to a tail section having a longer chord than normal. This also provides a very long vertical steering surface (rudder), which is believed to be unique to die present design. Modeling studies (discussed infra) of the aircraft have indicated that the unusual span of the rudder does not detract from die performance of the aircraft or lead to undesirable flying characteristics. Referring to Figure 3, the aircraft of Figure 1 is depicted in flight, with the wing extension panels (4 and 5) fully extended. The arc of the propellers (8 and 9 in Figure 1) is depicted by circles (labeled 8 and 9 here). The forward landing gear (i.e., 21 and 29 in Figure 1) are not visible in this figure, having been fully retracted into the nose section. Similarly, the curved mounting armatures (6 and 7) are pictured here pivoted to a position such that the rear landing gear (i.e., 19, 20 and 23 in Figure 1) are retracted and housed widiin the fuselage section (300) under the wing, and the lower portion of the port armature (7) is seen to nest in the fuselage, flush with the outer surface of the main fuselage section (300). The upper portions of both curved mounting armatures (6 and 7) are pictured here pivoted to a position such that the mounted propellers (8 and 9) are at the level of the wing, and the armatures (6 and 7) are nesting in wing recesses such that the outer surfaces of the armatures (6 and 7) form flush, continuous surfaces with the surface of the main wing section (1). All other aspects of this figure are as depicted in Figure 1. Referring to Figure 4, the aircraft of Figures 1 and 2 is shown in flight, with the wing extension panels (4 and 5 in Figure 1) fully retracted and housed within the main wing section (1). In this configuration and in this port side perspective view, the only part of either wing extension panel visible is the port wing extension panel tip (37), seen here mated with the port fixed wing tip (39) to form an aerodynamic teardrop wing tip. All other aspects of this figure are as depicted in Figure 3. Referring to Figure 5, an aircraft substantially identical to the aircraft of Figures 1 and 4 is shown in flight, with the wing extension panels (4 and 5 in Figure 1) fully retracted and housed within the main wing section (1). In this configuration, the cabin extension module and upper cabin extension assembly (2) shown in previous figures have been removed, resulting in a shorter fuselage and a decrease in overall aircraft weight. In embodiments of this invention where (as here) the engines are mounted inboard, on the centerline of the aircraft and under the wings, modification of the fuselage in the manner illustrated can be accommodated in the manufacturing steps by simply substituting lighter engines to redistribute the weight of die aircraft. No general re-design of die aircraft is necessary, and no retooling of the manufacturing process must be done. As in Figure 4, the only part of either wing extension panel visible is the port wing extension panel tip (37), seen here mated with the port fixed wing tip (39) to form an aerodynamic teardrop wing tip. All other aspects of this figure are as depicted in Figure 4. Referring to Figures 6 and 7, an aircraft according to the invention is shown in frontal elevation, viewed nose-on. The aircraft incorporates the compound wing assembly discussed supra, comprising main wing structure (1) and telescoping extendable wing sections (4 and 5). As pictured, the fixed wing section (1) also comprises leading edge slats (14 and 15) and teardrop or bullet-shaped wing tips (38 and 39). The wing extension panels (4 and 5) are also pictured with leading edge slats (16 and 17) and wing tip caps (36 and 37), which mate widi the fixed wing tips (38 and 39) to form aerodynamic teardrop wing tips, when the wing extension panels (4 and 5) are fully retracted within the fixed wing section (see, Fig. 7). Ailerons (10, 11) and flaps (72) are also shown. The aircraft illustrated in Figures 6 and 7 also incorporates curved mounting armatures (6 and 7), pivotally attached to the roots of the wings, each armature comprising an upper end and a lower end with respect to the pivotal attachment, die upper end of each armature being equipped and configured to accept a propeller assembly or to act as a propeller mount, and the lower end of each armature being equipped and configured to accept or to act as a mount for a compound landing gear comprising stabilizing wheels (18 and 19) and pontoon members (22 and 23). Propellers (8 and 9) are shown mounted on the upper ends of the armatures (6 and 7). The position of the ends of the mounting armatures in relation to the fuselage of the aircraft (i.e., the degree of rotation about the pivotal attachment) is preferably controlled by means of multilink actuating struts (280 and 281). Extension of die struts (280 and 281) pivots the armatures so that die upper end of each armature (6 and 7) and dius the propeller mounts are rotated upward from the level of the wing and inward toward die centerline of the fuselage; extension of the struts (280 and 281) simultaneously pivots the armatures so that the lower end of each armature (6 and 7) and dius the compound landing gear (18, 19, 22, 23) are rotated outward from the fuselage. At an intermediate point of extension (shown) of the actuating struts (280 and 281), die armatures are in a position wherein the stabilizing rear landing wheels (18 and 19) are swung into the proper orientation to assist in supporting the aircraft during a hard- surface landing. At full extension (not shown here) of die actuating struts (280 and 281), the armatures (6 and 7) are rotated to a position where the upper ends of the armatures and the propeller mounts are at a maximum distance above the wing structure (1) and die pontoon members (22 and 23) of the compound landing gear are in the proper orientation to assist in supporting the aircraft during an amphibious landing. The armatures (6 and 7) are preferably shaped so that when the actuating struts (280 and 281) are fully retracted, the upper ends of die armatures (6 and 7) nest in recesses (not shown) in the fixed wing section (1), with one surface of each armature becoming flush widi the aerodynamic surface of the wing and forming part of the airfoil, and the lower ends of the armatures (6 and 7) nest in recesses (not shown) of the fuselage, with the outer surface of lower end of each armature becoming flush with the surface of the fuselage. Forward landing gear are also illustrated in Figures 6 and 7 and are also compound, comprising a steerable forward landing wheel (21) and forward skis (29). The forward landing gear (21, 29) are fully retractable within the nose section of the fuselage, and preferably the lower surfaces of the skis (29), when retracted, form part of the surface of the fuselage and thus do not create any external drag during flight. Steerable rear landing wheels (20) are also depicted in Figures 6 and 7, however they are partially hidden in this view by the forward landing wheel (21). (See, Figures 56 and 58, item 20.) Referring to Figures 8, 9 and 10, an aircraft similar to that depicted in Figure 6 is shown, except that in these figures positioning of the compound landing gear in orientations appropriate for snow landing/takeoff (Figure 8), water landing/ takeoff (Figure 9), and slow taxiing in water (Figure 10), respectively, are illustrated. In Figure 8, a frontal view is shown of the forward skis (29) and the rear skis (114), deployed to a position where they are acting as the primary landing gear for the aircraft. All other aspects of Figure 8 are as illustrated in Figure 6. In Figure 9, a frontal view is shown of the pontoon members (22, 23), rotated into proper position to act as stabilizing outriggers during a water landing. This positioning of the outrigger pontoons (22, 23) is effected by full extension of the multilink actuating struts (280, 281). Note that full extension of the multilink actuating struts (280, 281) causes the stabilizing rear landing wheels (18, 19) to be retracted into recesses in the lower end of the armatures (6 and 7). The primary landing gear for the aircraft in such an operation is the hull-like fuselage, the forwardmost section of which is visible in this frontal elevation. The hull fuselage of the embodiment of Figure 9 has a pronounced "V" shape in cross-section (high deadrise angle). In contrast to shallower hull designs, the V-shaped hull improves handling of the aircraft in choppy water and lowers the G load on d e hull during water landings. All other aspects of Figure 9 are as illustrated in Figure 6. Figure 10 presents the same view of the aircraft as in Figure 9, except that the auto- retracting rear stabilizing wheels (18, 19) have been partially lowered and the lower ends of the armatures (6, 7) have been rotated slightly downward and inward by articulation of die innermost link of each of the multilink actuating struts (280, 281). Flotational elements (18, 19, 22, 23) have thus been forced downward against the surface of the water, thereby leveling the aircraft and improving the taxiing performance of the aircraft at slow speeds on water. All other aspects of this figure are the same as in Figure 6. Referring to Figures 11 and 12, an aircraft according to the invention and as depicted in Figures 6 and 7 is shown in frontal elevation, with the extendable wing panels (4 and 5 in Figure 12) fully retracted in Figure 11, so that the wing tip caps (36 and 37) are mated with the fixed wing tips (38 and 39) to form aerodynamic teardrop wing tips, and with the extendable wing panels fully extended in Figure 12. The main wing structure (1), the leading edge slats (14, 15, 16 and 17), the forward section with upper cockpit assembly (3), and die propellers (8 and 9) all are as depicted in Figures 6 and 7. The forward skis (29) are illustrated in Figure 11 in their fully retracted position, wherein die lower surface of the skis is flush with the fuselage surface. It is an especially preferred aspect of aircraft according to this invention diat all landing gear may be fully retracted within the fuselage, out of the airstream, and that landing gear doors (and their associated mechanisms) may be eliminated, since the ski elements are preferably designed to merge with the fuselage. The landing gear designs disclosed herein are believed to be the first designs that combine full retractability of all landing gear elements (wheels, skis and pontoons) and elimination of gear-enclosing doors from the fuselage. Referring to Figures 13, 14 and 15, die principal aspects of the compound wing structure of die present invention are shown in plan. All elements depicted in Figures 13, 14 and 15 are as described in Figures 4, 1 and 3, respectively. (See, also, Figures 12, 6 and 11.) The Compound Wing One of the principal inventive features of this invention is a compound wing. Aircraft incorporating this feature have the capability of being structurally modified, in flight, at the option of die pilot, so as to exhibit a wide range of flight characteristics or to adopt to a wide variety of flight conditions. In other words, aircraft incorporating the compound wing can be made to behave, aerodynamically, like several different types of aircraft, by the extension or retraction of extendable wing panels laterally from a central fixed wing section, as discussed supra. Aircraft of improved performance, versatility and safety are the result. The compound wing feature and possible mechanisms for its operation are illustrated in Figures 16 through 33. Figure 16 shows the construction of a starboard wing extension panel (4). Previously discussed external features such as the teardrop wing tip cap (36), the leading edge slat (16) and the aileron (12) are shown. In this figure, the outer skin (26, e.g., of flush riveted aluminum) of the panel (4) is shown cut away to reveal internal support structures, such as structural ribs (27), reinforcing stringers (28), a forward lift spar (30), and a rear or aft lift spar (32). All such structures are typically constructed of aluminum, fastened together by rivetting. The wing extension panel (4) also features a drag spar (34) positioned between die two lift spars (30 and 32). All of the spars (30, 32, 34) extend the entire length of the extension panel and roughly an equal length from the root of the wing extension panel (4). A guide bar (116) attached to die drag spar (34) provides a means for guiding the extension/retraction movement of the extension panel (4) relative to the fixed section of the wing (not shown). Figure 17 shows a more detailed view of the encircled portion XVII of Figure 16. Lift and drag spars 30, 32 and 34 are seen to have an 'T'-beam shape, characterized by flange (79) and web (80) portions. At the end of the lift spars (30 and 32), beam end guide blocks (117) are attached (e.g., riveted) into the area between the flanges (79) on one side of each spar (the forward side, in this figure); similarly, on the drag spar (34), a beam end guide block (118) is attached (e.g., riveted) in the area between the flanges (79) on one side of die drag spar (34) (here, the upper side). Pairs of guide rollers (115) are rotatably attached to each of die beam end guide blocks (117, 118). The lift spar guide rollers (117) are positioned so as to provide a roller guide that will be in communication with the inside of lift spar flanges of a port wing extension panel. Similarly, the guide rollers (115) fixed to die drag spar beam end guide block (118) are positioned to accept and provide a rolling guide for a guide bar fastened onto die drag spar of a port wing extension panel assembly (not shown), which port extension panel guide bar would correspond to die pictured starboard drag spar guide bar (116). The drag spar guide bar (116) is positioned to be accepted by a beam end guide roller system on a port wing extension assembly. This system of guide rollers and bars maintains die proper interlocking alignment of the support spars of port and starboard wing extension assemblies. Preferably, the drag spar guide bar (116) and its associated roller guides will have an interlocking tongue-and-groove shape, which will reduce any vibration. Although the system of roller guides and bars just described is not critical to the compound wing (i.e., the port and starboard wing extension panels' spars may simply be in slidable interlocking contact), die described system of guides (or its equivalent) will ensure smooth operation of the moveable panels of the compound wing, will decrease vibration of the spars, and will minimize die possibility of the panels jamming in flight. Whereas Figures 16 and 17 illustrate the relative positions of die two wing extension panels (4 and 5 in Fig. 1) of the compound wing, Figures 18 and 20 show die position of the starboard wing extension panel (4) relative to the fixed wing section (1, in phantom lines), and show a preferred system of guide rollers for maintaining the position of the extension panels relative to the central fixed wing section. Referring to Figure 18, a starboard wing extension panel (4), with wing tip (36), leading edge slat (16), trailing edge aileron (12), and supporting spars (30, 32, 34), is shown in similar aspect to iat of Figure 16. In phantom (dotted) lines, approximately half of the fixed wing section (1) of the compound wing is shown, extending from fixed wing tip 38 to the centerline C (dashed line), denoting the central plane of the aircraft to which the wing section (1) is attached. The portion of the fixed wing section (1) shown here includes an aileron (10) and a flap (72). As shown in this illustration, the starboard wing extension panel (4) is in sliding communication with the fixed wing section (1): The extension panel (4) is pictured at full extension from the distal end of the fixed wing section (1), and die entire assembly (e.g., 4, 12, 16, 30, 32, 34, 36) is capable of sliding as a unit inward toward the root of the fixed wing (i.e., toward centerline C). A plurality of extension panel positioning rollers (40, 42, 44, 46, 48, 50), which are fastened to die inside of the fixed wing section (1) at the distal end, is positioned in relation to die wing extension panel (4) to snugly hold the extension panel (4) while permitting (by rolling) extension and retraction of the panel (4) along the longitudinal axis of the wing section (1). Additional guide rollers (52 and 54) may be provided in association with some alternative mechanisms for co-actuation of the extension panel ailerons and die fixed wing section ailerons. (See, Figure 30.) In embodiments using cable or rod co-actuation mechanisms, such additional guide rollers (52 and 54) may be eliminated. (See, Figures 33 and 32.) A further plurality of supporting spar positioning rollers (unnumbered, widiin encircled area XIX) secures and positions the wing extension assembly along the centerline (C), where the starboard support spars (30, 32, 34) mesh with the series of support spars (31, 33, 35) of the port wing extension assembly of the compound wing. Referring to Figure 19, which is a more detailed view of encircled portion XIX of Figure 18, the meshing juxtaposition of die port (31, 33, 35) and starboard (30, 32, 34) supporting spars of the port and starboard wing extension assemblies is illustrated. (Elements such as guide rollers and end guide blocks (i.e., items 115-118 in Figure 17) have been omitted here for clarity.) Each spar is secured and guided by a pair of rollers, which are attached to the fixed wing structure (not shown): SPAR ROLLERS port lift spar 31 57 and 61 starboard lift spar 30 56 and 60 port drag spar 35 65 and 67 starboard drag spar 34 64 and 66 port lift spar 33 59 and 63 starboard lift spar 32 58 and 62. Taken together, the series of rollers (40, 42, 44, 46, 48, 50, 52, 54, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67), and additional rollers (port side) not illustrated in Figures 18 and 19, secure the moveable wing extension assemblies within the fixed wing structure of the compound wing, ensure smooth, rolling operation of both wing extension panels simultaneously, and maintain the proper alignment of the wing extension panels in relation to the fixed wing section. Figure 20 shows this series of rollers in spatial relationship, with the relative positions of the fixed wing structure (1), starboard wing extension panel (4) and port wing extension panel (5) depicted in phantom lines (wing extension panels fully retracted). Preferably, the positioning rollers described above will be made of metal, e.g., aluminum, coated with a thin plastic or rubber skin. A further illustration of the position and operation of the rollers is provided by Figures 21, 22, and 23. Figure 21 provides a cross-sectional view of the forward lift spar (30) and wing extension panel (4) of die starboard wing extension assembly (see, Fig. 16) and its position relative to die fixed wing structure (1), as maintained and secured by roller elements (e.g., 40, 44, 56, 60). Figures 22 and 23 illustrate the operation of the compound wing, wing extension panel (4) is retracted as a unit toward centerline (C). The wing extension panel (4) is fully retracted in Figure 23, where the extension panel wing cap (36) mates with die fixed wing tip (38), and die entire wing extension panel (4) is enclosed within die fixed wing structure (1). The cooperative construction of the compound wing is further illustrated in Figures 24, 25 and 26, which show various sectional views through starboard wing structures (ref. Figures 13 and 15, section lines A-A, B-B and C-C). Referring to Figure 24, a sectional view taken on line A-A of Figure 13 shows the structures of the starboard wing extension panel (4), as viewed along its longitudinal axis toward die wing tip cap (36). Several previously described features of the starboard wing extension panel (4) are seen in cross-section: The leading edge slat (16) (fixed in position by one or more structural rib extensions (73)), aileron (12) (pivotally attached at one or more points to the wing extension panel (4) at structural rib extensions (74) through bearings (75), forward lift spar (30), drag spar (34), and aft lift spar (32). Guide bars (116) are visible in this figure not only on die drag spar (34) but also on the web of the two lift spars (30 and 32). Figure 24 further shows reinforcing stringers (28), which run substantially the entire length of the wing extension panel (4) and are riveted to die underside of die outer skin (26) of the panel. Figure 24 additionally shows clearance holes 76, 78, and 77, which are provided to accommodate the corresponding forward lift spar, drag spar, and aft lift spar, respectively, of a port wing extension panel as the two extension panels slide togedier within the fixed wing structure of the compound wing. (See, Figure 26.) Referring to Figure 25, a sectional view taken on line B-B of Figure 13 shows the structures of the starboard wing extension panel (4), as viewed in a fully extended position, looking spanwise, toward the wing tip, from a point just inboard of die fixed wing tip (38). Several previously described features of the compound wing are seen in cross-section: The leading edge slats (14, 16), structural rib extension (73), positioning rollers (40, 42, 44, 46, 48, 50), guide bars (116), panel skin (26), stiffening or structural rib (27), ailerons (10 and 12), structural rib extension (74), bearing fastener (75), guide rollers (52 and 54), forward lift spar (30), aft lift spar (32), drag spar (34), and clearance holes (76, 77 and 78). Additional structures of the fixed wing section are also visible in Figure 25, i.e., fore and aft supporting spars (68 and 69, respectively). Referring to Figure 26, a sectional view taken on line C-C of Figure 15 shows the structures of the starboard wing extension panel (4), as viewed in a fully retracted position, looking spanwise toward die wing tip, from a point just inboard of the fixed wing tip (38). Referring momentarily to Figures 13 and 15, it will be appreciated that in contrast to the view in Figure 25, the view of Figure 26 is taken when die wing extension panels (4 and 5 in Fig. 13) are fully retracted, and dius many of ie associated internal support structures are intermeshed. Previously described features of the compound wing seen in Figure 25 are also seen here in cross-section: The leading edge slats (14, 16), structural rib extension (73), positioning rollers (40, 42, 44, 46, 48, 50), guide bars (116), panel skin (26), stiffening or structural rib (27), ailerons (10 and 12), structural rib extension (74), bearing fastener (75), guide rollers (52 and 54), forward lift spar (30), drag spar (34), aft lift spar (32), main wing supporting spars (68 and 69), and clearance holes (76, 77, 78). Additional structures, i.e., from a port wing extension assembly that have retracted into this sectional view of the starboard wing, are now seen: The forward lift spar (31), with associated end block (117) and guide rollers (115), which are in rolling communication with the guide bar (116) fastened to the web of die forward lift spar (30) of the starboard wing extension assembly; die port drag spar (35), with associated end block (118) and guide rollers (115), which are in rolling communication with the guide bar (116) fastened to die web of de starboard drag spar (34); and the aft lift spar (33), with associated end block (117) and guide rollers (115), which are in rolling communication widi the guide bar (116) fastened to d e web of the aft lift spar (32) of the starboard wing extension assembly. From Figures 25 and 26 it will be appreciated diat clearance holes (76, 77, and 78) are cut in each of die structural ribs (27), which are spaced approximately 1-1 X Δ feet apart for the length of each of die wing sections, in accordance widi conventional wing construction. These passages (76, 77, 78) are sized and positioned to permit die wing extension spars (31, 33, and 35) of die port wing to pass through substantially die entire length of the starboard wing extension panel (4). Similar clearance holes will exist in each of the structural ribs of the port wing extension assembly. Further detail of ie relative positions of the overlapping spars is shown in Figure 36. Extension and retraction of the wing extension panels may be effected by any means that reliably moves both panels simultaneously. Differential extension or retraction of the panels which results in bilaterally asymmetrical wing span will increase yaw and result in loss of directional control. Several suitable me iods for actuating die components of die compound wing described herein will be apparent to diose skilled in die art, however by way of illustration Figures 27, 28, and 29 depict two suitable mechanisms. Figure 27 depicts a cable system for retracting and extending die wing extension panels. In phantom lines, die starboard side of die fixed wing structure (1) is shown enclosing die lift and drag spars (30, 32, 34) of the starboard wing extension panel (4), and the extension panel (4) is fully extended. Also shown in phantom lines are the opposing lift and drag spars (31, 33, 35) of the port wing extension panel. In the system illustrated here, extension and retraction of the wing extension panels is controlled by two control cables (158 and 159). Optional coordinating cables (301 and 302) may also be provided as a safety measure, to ensure that the port and starboard wing extension panels will always be extended or retracted to substantially the same degree. One end of control cable 158 is attached to die starboard forward lift spar (30) near the base of the wing extension panel (4). The cable (158) is threaded dirough a pulley (161) rotatably fixed to die fixed wing structure (1), through an anchor block (304), through another pulley (161) attached to die fixed wing section (1), and die other end of the cable (158) is attached to the opposing port forward lift spar (31) near the base of die port wing extension panel (not shown). The anchor block (304) is attached to a specific point of die cable (i.e., die midpoint), and die control cable (158) cannot slide urough the anchor block (304). Alternatively, of course, two cables could be employed wherein one end of each cable is attached to die anchor block (304) and die other end of each cable is attached to die port or the starboard lift spar near die base of the respective wing extension panels. The second control cable (159) is attached at one end of die starboard lift spar (30), threaded through a pulley (161) rotatably attached to the fixed wing structure (1), through an anchor block (303), through another pulley (161) rotatably attached to die fixed wing structure (1), then attached to die end of the opposing port lift spar (31). Again, die single control cable (159) may alternatively be substituted with two cables, both attached to the anchor block (303) at one end and dien attached respectively to either the port or starboard lift spars. A belt or chain (160) is attached to anchor block 303 at one end, threaded around a drive pulley (162), and attached at the other end to anchor block 304. The belt (160) is driven by the drive pulley (162), which, in turn, is controlled by a motor or mechanism (not shown) attached to the main wing structure (1). In operation, when the drive pulley (162) is rotated counterclockwise, control cable 158 is pulled, and control cable 159 is relaxed, thereby drawing the wing extension assemblies togedier (retracting the wing extension panels). When the drive pulley (162) is rotated clockwise, control cable 159 is pulled and control cable 158 is relaxed, thereby extending the wings. The arrows in Figure 27 show the direction of movement of the cables (158, 301, and 302) when the drive pulley (162) is turned counterclockwise and die extension panels are retracted. Because asymmetric extension or retraction of the wing extension panels, e.g., due to a control cable failure, would cause a loss of control characteristics, an optional fail-safe mechanism for keeping the movement of the wing extension panels coordinated may be employed and is illustrated in Figure 27. Two coordinating cables (301 and 302) are utilized: Cable 302 is attached at one end to the middle of the starboard aft lift spar (32) near the base of the starboard wing extension panel (4), threaded around a pulley (164) which is attached to die fixed wing section (1), dien attached at its other end to the end of die port aft lift spar (33); and similarly, cable 301 is attached at one end to the middle of die port aft lift spar (33) near the base of the port wing extension panel (not shown), threaded around a pulley (164) which is attached to die fixed wing section (1), dien attached at its other end to the end of starboard aft lift spar (32). In the event that any of the control cables (158, 159) fails, the coordinating cables (301, 302) would ensure that die degree of extension or retraction of the port and starboard wing extension assemblies would be substantially die same. Figure 28 is a detailed view of encircled portion XXVIII of Figure 27. All of the features (drive pulley (162), anchor blocks (303, 304), control cables (158, 159), drive belt (160), pulleys (161, 164), starboard and port lift spars (30, 31, 32, 33), starboard and port drag spars (34, 35), and coordinating cables (301, 302)) are as described above. Arrows in uiis figure show the direction of movement of the adjacent structure (pulley, spar, or cable) as the wing extension panels are retracted by counterclockwise drive of the drive pulley (162). Alternative methods for actuating a cable control system such as that of Figures 27 and 28 will be apparent to those skilled in iis art. For example, the anchor blocks (303 and 304) could be attached to threaded nuts at either end of a leadscrew, instead of being attached by a drive belt (160) as illustrated Referring to Figure 29, an alternate method of extending and retracting the wing extension panels is shown. Most of the structural items of this figure have been described previously and are the same as illustrated in Figure 27. Instead of the cable control system of Figure 27, however, there is a leadscrew (217) that extends from tip to tip of the fixed wing section (1). One end is threaded with a right hand diread and the other end has a left hand diread. An appropriately threaded leadscrew nut (218) is attached to the wing extension panel (4), and a leadscrew drive motor (219) is provided that is capable of rotating the leadscrew in bodi clockwise and counterclockwise directions. Operation of the drive motor (219) causes the leadscrew nut (218) to be pushed outward or pulled inward, depending on the rotation of the leadscrew, with a consequent extension or retraction of the wing extension panel (4). The final aspect of the innovative compound wing of the present invention that must be addressed is die co-actuation of the ailerons of the fixed wing and of die wing extension panels. If the extension panel ailerons do not operate in concert with the fixed wing ailerons, the airplane becomes much more difficult to control. Accordingly, the full advantages of the compound wing described herein will not be realized without adopting some mechanism for co- actuation of the ailerons. Several mechanisms will suggest themselves to those skilled in the art, and diree such mechanisms are illustrated in Figures 30, 31, 32, and 33. Referring to Figure 30, which is a cross-sectional view taken along line J-J of Figure 15, a partial view is shown of a starboard wing extension panel (4) retracted within the fixed wing structure (1). Several of the structural elements such as support spars, clearance holes, and guide bars and rollers have been described previously and are the same as depicted in previous figures (see, e.g., Figure 26). An additional feature shown in this figure is an aileron actuator plate (85) fastened to the fixed wing structure (1) by actuator plate guides (87), which permit sliding reorientation or pivoting of the actuator plate (85) along guide slots (86) cut in the plate, in response to conventional actuation of the fixed wing aileron (10), through connecting arms (88 and 89). The aileron actuator plate (85) also acts as a housing for two guide rollers (52 and 54), which are in rolling communication with the extension panel aileron (12). It is readily seen diat movement of the fixed wing aileron (10) is automatically translated via the aileron actuator plate (85) and the guide rollers (52 and 54) to the extension panel aileron (12); and because the aileron actuator plate (85) is in contact with die extension panel aileron (12) through rollers (52 and 54), the action of the fixed wing aileron (10) is translated to die extension panel aileron (12) during extension or retraction and regardless of the degree of extension or retraction. Figures 30 and 31 show two views of the same wing structures. In Figure 30, the ailerons (10 and 12) are raised; and in Figure 31, ailerons (10 and 12) are lowered. Comparison of these two figures illustrates the pivoting reorientation of the aileron actuator plate (85) and associated linkages (88 and 89). Referring to Figure 32, a preferred method of actuating the wing extension aileron in concert with the fixed wing aileron is shown. The fixed wing ailerons (10) are controlled by movement of a sliding actuator bar (103), which movement is translated to the fixed wing aileron (10) through a conventional arrangement of bellcranks and rods. The actuator bar (103) runs through bar guides (122), which are fixed to die fixed wing section (1) along the centerline of the fuselage. The flaps are controlled by means of a control rod (307), the movement of which is translated to die flap (72) through conventional linkages. It is often advantageous to co-actuate flaps and ailerons to increase lift (drooped ailerons) or increase roll control (flaperons). Figure 32 illustrates a system wherein, if control rods 306 and 307 are co-actuated (i.e., under control of the flap lever), then aileron (10) will assist the action of the flap (72). For co-actuation of the extension panel aileron (12) in concert with the fixed wing aileron (10), Figure 32 illustrates a cable system controlled by the same sliding control bar (103) diat actuates the linkages to the fixed wing aileron (10). In this embodiment, an aileron actuator cable (105) is attached at one end near the end of the forward lift spar (30), threaded through an actuator guide pulley (101) rotatably attached to the fixed wing structure (1), through an aileron control pulley (157) rotatably attached to the control bar (103), through another actuator guide pulley (101) rotatably attached to the fixed wing structure (1), through another guide pulley (104) rotatably attached to the lift spar (30) near the base of the wing extension panel (4), then attached at its other end to a sectioned pulley (100) fixedly attached to the extension panel aileron (12). A second aileron actuator cable (106) is attached at one end of the sectioned pulley (100), direaded through a guide pulley (104) rotatably attached to die aft lift spar (32), through an actuator guide pulley (101) rotatably attached to the fixed wing section (1), dirough an aileron control pulley (157) rotatably attached to the aileron control bar (103), through anodier actuator guide pulley (101) rotatably attached to the fixed wing structure (1), then attached at its other end near the end of die aft lift spar (32). It will be appreciated from Figure 32 that when the sliding control bar (103) is moved, this arrangement of cables (105, 106) and pulleys (101, 104, 157) causes one cable (i.e., 105 or 106) to slacken while the odier cable tightens with respect to the sectioned pulley (100), which causes that pulley to rotate and thus raise or lower the extension panel aileron (12) accordingly. It will also be appreciated that as the wing extension panel (4) is retracted, the entire wing extension assembly, including the starboard lift spars (30 and 32) will roll inward, across the longitudinal axis of die control bar (103), but the relationship of the cables (105, 106), control bar (103), sectioned pulley (100) and aileron (12) is preserved: As the lift spars (30 and 32) roll across the longitudinal axis of the control bar (103), the actuating cables (105 and 106), which are attached to the ends of the lift spars (30 and 32) will move as a unit widi the lift spars (30 and 32), sliding through the arrangement of pulleys (101, 157) but not altering the ability of control bar movements to be directly translated to the panel aileron (12). A corresponding actuating system for the port side extension panel aileron is indicated in Figure 32 by the corresponding cables (120 and 121) attached to the port fore and aft lift spars (31 and 33), the ends of which are indicated by phantom lines. The arrows in Figure 32 show the direction of movement of the components of the system when the control bar (103) is moved forward. The bellcranks, rods, pulleys and cables depicted in Figure 32 are all of standard construction and are typically fabricated of stainless steel. The size (diameter) of the pulleys (100, 101, 104, 157) and positioning of the aileron control pulleys (157) with respect to the actuator guide pulleys (101) fixed to the wing section (1) will be calculated so that the amount of cable slack paid out or taken up by movement of the control bar (103) does not exceed die amount of cable required for the entire range of movement of the aileron (12). Viewed another way, it will be kept in mind that in the arrangement of cables and pulleys illustrated here, if the aileron control pulleys (157), moving with the control bar (103), are taken up to or beyond the point of alignment with the spar guide pulleys (101) dirough which the associated cable (e.g., 105, 106) is threaded, the aileron control pulley (157) would no longer be in effective contact with its associated cable, and movement of the control bar (103) would no longer affect the tension of the actuation cables (105, 106). Pulleys accordingly will be sized and positioned in relation to each other so as to maintain control of the ailerons. Referring to Figure 33, an alternative system for co-actuation of the fixed wing aileron (10) and die extension panel aileron (12) is shown. In this system, cable linkages are responsible for actuation of all ailerons (10, 12) and flaps (72), rather than a combination of cable linkages and control rods, bars and bellcrank-type joints. (Cf. Fig. 32.) The actuation system for the extension panel aileron is essentially as depicted in Figure 32. For actuation of the starboard fixed wing aileron (10) and starboard flap (72), the control bar (103) is connected to the fixed wing aileron (10) via two cables (124 and 125). Cable 124 is fastened at one end to the control bar (103), threaded through an inner aileron actuator pulley (123) rotatably fastened to a pivoting master flap actuator plate (156) (controllable by the pilot by a mechanism not shown here), through an aileron guide pulley (108), then fastened at die other end to a sectioned pulley (107) fixedly attached to the aileron (10). Cable 125 is similarly attached, in opposing fashion with respect to cable 124, as shown in Figure 33. A sectioned pulley actuating plate (155) fixed to the main wing flap (72) is similarly attached, via two cables (308 and 309), through guide pulleys (154) to the pivoting master flap actuator plate (156), as shown. In operation, pivoting of the master flap actuator plate (156) by the pilot causes the flap (72) and the main wing aileron (10) to move together. Fore-aft movement of the actuator control ion wing aileron (12) to move in concert. A corresponding actuating system for the port side extension panel and fixed wing section ailerons is indicated in Figure 33 by the corresponding cables (120 and 121 for the wing extension panel aileron; 126 and 127 for the fixed wing section aileron) attached to the port fore and aft lift spars (31 and 33) and the master flap actuator plate (156), respectively. As in Figure 32, the inboard end of a port wing extension panel assembly is depicted in phantom lines. The arrows in Figure 33 show the direction of movement of the components of the system when the control bar (103) is moved forward. The Engines and Belt-Driven Propellers Preferred aircraft according to the present invention will employ an innovative power train and means of propulsion incorporating two engines, mounted inboard (i.e., within die fuselage on the centerline of the aircraft), which drive (via a system of drive belts) two pusher- type propellers mounted on the wing or, most preferably, on mounting armatures such as described previously that permit the position of the propellers to be changed at the option of the pilot. This propulsion system not only harmonizes with other aeronautical discoveries described herein, such as the bilaterally extendable compound wing, the pivoting mounting armatures and the multi-purpose compound landing gear, but also eliminates many safety hazards unavoidable in conventional multi-engine aircraft, improves the efficiency of the airfoil, eliminates gravity loads that conventionally must be borne by the wings, offers greater protection to the engines and lowers die aircraft's center of gravity while utilizing space normally wasted in conventional aircraft, and virtually eliminates the dangers ordinarily associated with unexpected failure of one engine. According to die present invention, two engines are mounted in die fuselage of the aircraft, in tandem and in opposed relation, immediately aft of the cabin section, under the wings. Referring momentarily to Figure 51, which is a cross-sectional view of the midsection of an aircraft according to die invention, two aircraft engines (24 and 25) are seen in silhouette. Air-cooled aircraft engines, such as the six-cylinder, horizontally opposed Lycoming IO-540, are suitable, however water-cooled automobile engines, such as a GMC 454-cubic inch V-8 engine, would also be suitable. The engines are preferably mounted, using conventional rubber engine mounts, to a steel frame, which frame is bolted to the fuselage. This permits easy removal of the engines for servicing or replacement. Moreover, if changes occur in the specifications for the engines (or changes occur in regulations governing the power requirements), the engines can be switched widiout the necessity of designing new external engine mounts, fairings or nacelles, and without refiguring the physics of the airfoil. Thus, even where the aircraft is in mass production, a complete alteration of the power plant can be implemented without interruption of the production line or retooling of production machinery. Mounting two engines in opposed relationship permits the propellers to be driven in opposite directions (counter-rotating propellers), without requiring one engine to be a custom- made counter-rotating engine. There are several disadvantages to multi-engine aircraft with propellers that turn in the same direction. Such aircraft have a tendency to yaw in one direction (left or right) for several reasons rooted in the same-direction motion of the propellers: Reaction of the aircraft to the torque required to turn the propeller, asymmetric thrust due to unequal angles of attack of the upward-turning and downward-turning blades, the effect of the twisted air flow behind the propeller, and gyroscopic turning moments. All of these forces tend to compromise the controllability of the aircraft, and die negative traits can be amplified where there is a differential power output to the propellers. In an aircraft according to die invention, two identical engines can be used to drive two oppositely rotating propellers, and the disadvantageous reaction to torque, asymmetric thrust and gyroscopic turning moment resulting from one rotating propeller are all cancelled by the opposite forces of a counter-rotating propeller. The turbulence behind die propellers is also balanced, and the aircraft rotational inertia is minimized by placing die items of greatest mass (the engines) near the center of gravity. In addition, since die engine mass is near the center of the fuselage rather than on the wings, the center of gravity is lower, which is especially beneficial to amphibious aircraft for taxiing and performing other operations on the water. In conventionally designed multi-engine propeller aircraft, the engines are housed in nacelles on the wings. Although d e nacelles are shaped to be as aerodynamically harmless as possible, there is no escape from the fact the area of the wing surface taken up by the nacelles and aft of the nacelles provides no lift, and the nacelles diemselves create drag. These disadvantages are eliminated by placing die engines inboard and modifying the wing surface only to the extent necessary to accommodate die propeller mounts. The efficiency of die airframe is thus improved. Conventionally mounted propeller/engines on a multi-engine aircraft must be located far enough from the longitudinal centerline of the aircraft for the propellers to clear the sides of the fuselage. This distance off the centerline makes conventional multi-engine aircraft difficult to control in the event of an engine failure, which requires immediate correction of the asymmetric thrust provided by die live engine(s) and sudden drag of die dead propeller/engine if uncontrollable spin or unintentional "wing-over" are to be avoided. These hazards are eliminated in aircraft according to the present invention, because by employing a system of overrunning clutches and a simple gearbox (see Fig. 37, discussed infra), the failure of one inboard engine will not lead to the failure of either propeller. Rather, the power from die engine that remains in service is transferred instantly to both propellers, requiring the pilot to adjust only to the power reduction and not requiring compensation for a sudden imbalance of thrust and responsiveness of the control surfaces. Referring to Figure 34, the midsection of the aircraft pictured in Figure 15 is shown in cross-section (view I-I). The relative position of the engines (24 and 25) to the fixed wing structure (1) and the fuselage (300) is seen. Figure 34 also shows, within the fixed wing structure (1), the intermeshed support structures of fully retracted starboard and port wing extension panels, including the forward lift spars (30, 31) and guide rollers (56, 57, 60, 61), starboard and port drag spars (34, 35) and guide rollers (64, 65, 66, 67), and starboard and port aft lift spars (32, 33) and guide rollers (58, 59, 622, 63). Support structures of the main fixed wing section (1) are also shown, including a forward main wing spar (68) and a rear main wing spar (69). The two engines (24 and 25) drive overrunning clutches (109) which allow torque (power) to be transmitted in one direction only (in this case clockwise). In the opposite direction the clutches (109) turn freely. The rear engine (24) and its overrunning clutch (109) drive a shaft (172) on which a belt pulley (96) (or, alternatively, a chain sprocket) is attached. The belt pulley (96) drives a cog belt (99) (or chain), which cog belt (99), in turn, goes on to drive mechanisms in the port wing not seen in this figure. In addition to driving the port belt pulley (96), die rear engine shaft (172) also drives a gear (184 in Fig. 37, discussed infra) inside a gearbox (110). In like fashion, die forward engine (25) and its overrunning clutch (109) drive a forward engine shaft (173), on which are attached a gear (187 in Fig. 37, discussed infra') in the gearbox (110) and a starboard belt pulley (95) (or, alternatively a chain sprocket). This belt pulley (95) drives a cog belt (99) (or chain), which runs to the starboard side of the wing as shown in Figure 34, and drives a pivot transfer pulley (94). The pivot transfer pulley is attached to a pivot transfer drive shaft (291) rotatably mounted in bearings (82) attached to a forward upper armature spar (70) and a rear upper armature spar (71). There is a co-axial armature pivot shaft (91) running through the length of the pivot transfer drive shaft (291) and extending fore and aft to armature pivot bearings (97), which are attached to the rear main wing spar (69) at the forward end and a rear auxiliary wing spar (98) at the aft end. The pivot transfer drive shaft (291) is therefore itself a tubular bearing, freely rotatable about a co-axial armature pivot shaft (91). Referring momentarily to Figure 1, it will be recalled diat the propellers (8 and 9) are preferably mounted on pivotally mounted armatures (6 and 7) that may be raised and lowered to change the position of the propellers relative to the wing (1). The cog belts (99 in Figure 34) driven by the inboard engines (24 and 25 in Figure 34) extend, in this embodiment, to the pivot points of the armatures where the engines' power is transferred to propeller drive belts extending into the upper ends of the armatures (6 and 7) to drive the propellers (8 and 9). Of course, in embodiments that do not incorporate the armature structures disclosed herein, the cog belts (99) may extend directly to pulleys attached to propeller shafts mounted in die wings. As shown in Figure 34, the starboard cog belt (99) drives a transfer pulley (94) fixed to pivot transfer drive shaft (291), which extends from a forward upper armature spar (70) to a rear upper armature spar (71). Also attached to the pivot transfer drive shaft (291) is a pivot transfer drive pulley (93). The spinning of the pivot transfer drive shaft (91) and pivot transfer drive pulley (93) drive a propeller drive belt (84) (or, alternatively, a chain), which extends to a starboard propeller drive pulley and shaft (not shown). Alternatively, a single rotatable pivot shaft may be utilized in place of the co-axial shafts 91 and 291, but this is less preferred, since then a constantly rotating pivot shaft would be at the center of all the mounting armature pivot points. Another alternative would be to have a single stationary pivot shaft and to have both the cog belt (99) and the propeller drive belt (84) connected to a single freely spinning pulley mounted on the pivot shaft (replacing the transfer pulley (94) and the pivot transfer drive pulley (93)), or connected to separate pulleys which are fastened togedier. In the arrangement of drive belts shown in Figure 34, small idler pulleys (90) adjust and maintain a desired tension in the belts (84 and 99). Standard, commercially obtainable toothed belts (timing belts) constructed, e.g., of steel reinforced rubber, may be used throughout this system. In the most preferred embodiments, the components of the power train will be positioned so diat all four drive belts (2 x 84 and 2 x 99) are the same length. Likewise, standard toodied pulleys, shafts and bearings used in modern aircraft construction are suitable. Proper selection of the diameters of pulleys 83, 93, 94, 95, and 96 provide an overall speed reduction ratio that allows the engines (24 and 25) to run at a relatively fast speed (4400 rpm, for example), for optimum power production, while die propellers may turn at a relatively low speed, i.e., without approaching their maximum design speed (2700 rpm, for example). This propeller speed reduction eliminates the need for a costly speed reduction gearbox used on some existing aircraft engines. Incidentally, the positioning of the engines, cog belts and propellers as described above places these major sources of the aircraft's noise behind the cabin area. This will result in an aircraft that is comparatively quiet from inside die cabin, even though the engines are inboard. Figure 35 is a cross-sectional front elevation of the aircraft illustrating the relative positions of several components already discussed. The position in the fuselage (300) of the rear engine (24) is shown in solid lines; the position of the forward engine (25) is seen in dotted lines. This figure shows how the starboard and port cog belts (99) extend into the mounting armatures (6 and 7) to actuate the pivot transfer drive shafts (291), at the pivot points of the mounting armatures (6 and 7). Rotation of the pivot transfer drive shafts (291) causes propeller drive belts (84) to turn the starboard and port propeller drive pulleys (83), which are attached to the starboard and port propeller drive shafts (81), to which the starboard propeller (8) and port propeller (9) are attached. Through these belt and pulley linkages, the power of the engines (24 and 25) mounted inside the fuselage (300) is transferred to the propellers (8 and 9) mounted on die armatures (6 and 7) (or, alternatively, mounted in the wings). The positions of idler pulleys (90) is also shown in this figure. Figure 36 provides a plan view of the midsection of an aircraft incorporating the compound wing, mounting armatures and internal engine mounting features of the present invention. Nearly all of the structures pictured in Figure 36 have been described previously and have the same item numbers as in previous figures (see, e.g., Figures 1, 13, 16, 26, 34 and 35). The engines are represented in this figure only by the shafts 172 and 173 (see, Figure 34). Additional preferred auxiliary spars for the wing (98) and for the mounting armature (119) are shown here and were not included in previous figures. The interlocking relationship of the support structures of the extendable wing panels (4 and 5) is clearly shown in Figure 36. With die extension panels (4 and 5) in partial extension, as shown, the starboard and port forward lift spars (30 and 31), the starboard and port drag spars (34 and 35), and the starboard and port rear lift spars (32 and 33) are seen to overlap within the enclosing structure of the fixed wing section (1). From this figure it is seen that when the wing extension panels (4 and 5) are fully retracted widiin the fixed wing structure (1), each of the wing extension assemblies extends across nearly die entire (fixed) wing span, i.e., from wing tip to wing tip. Figure 36 also shows the plan of the drive belts (84 and 99) that transfer the power provided by the engines (represented here by shafts 173 and 172) to die propellers (8 and 9). Assuming clockwise rotation of the opposed engine shafts (172 and 173), die arrows in Figure 36 show the direction of die belts (84 and 99), which produces inwardly counter-rotating propellers. Inward counter-rotation of the propellers is preferred. As an added safeguard, the single drive belts (84 and 99) shown in Figure 36 and other drawings (e.g., 99 in Figs. 37, 38, 41) may be replaced with two, or more preferably three (or more) parallel drive belts, arranged side-by-side and separated by sheet metal dividers. The plural drive belts would provide continued power transfer to the propeller in the event of the failure of one belt. The dividers would prevent a failed belt from interfering with an operating belt. Referring to Figure 37, a diagram of the simple gearbox (110 in Figure 34) is shown. The gearbox permits power from one engine (24 or 25) to be automatically transmitted to bodi propellers, in the event of the other engine failing or being shut down. Disengaging die gears, by means of a gearing control arm (111), makes the rotation of the propellers completely independent. The gearbox (110) preferably houses five gears (184, 185, 186, 187 and 315). Gear 184 is driven by the rear engine (24); gear 187 is driven by die forward engine (25). The two gears 185 and 186 are idler gears, and gear 315 is an idler gear that can be moved along its shaft (see double-headed arrow) by means of the gearing control arm (111) while in motion. The moveable idler gear (315) can be positioned so diat it is disengaged from idler gear 185 (pictured), or it can be positioned so as to mesh via dogface sprockets (unnumbered) with gear 185. The idler gears 185 and 315 in Figure 37 may alternatively be replaced by a single moveable idler gear that can be moved to engage both gears 184 and 186. In the fully engaged position, the gears (184, 185, 186, 187 and 315) in the gearbox (110) cause the pulleys, belts, and propellers in this design to operate as one system (i.e., both propellers run at the same speed). With the gearbox disengaged, the front engine (25) and the port propeller (9 in Figure 36) and associated pulleys and belts run as a separate system from the rear engine (24) and die starboard propeller (8 in Figure 36) and associated pulleys and belts. In the disengaged configuration the aircraft operates much like a conventional twin- engine aircraft, at least in terms of the independence of the two propulsion systems. A great safety advantage is realized when the gears are engaged: The two propeller drive systems are connected by means of the gearbox to each other, so that if power from one engine should be compromised the odier engine would automatically provide power to both propellers evenly without requiring the pilot to take corrective action. Thus, with the gears engaged, a single engine shutdown does not lead, as in conventional multi-engine aircraft, to the aircraft being suddenly asymmetrically powered, and consequently the aircraft according to die invention acquire the performance advantages of multi-engine aircraft while achieving the operating simplicity of single-engine aircraft, and they realize the best of the safety characteristics inherent in each type of aircraft. The capability of unifying the power trains of all propellers through a simple gearbox as just described will have several carry-through advantages in subservient systems that may also be unified correspondingly. For example, in conventional engine/propeller systems, a separate propeller governor geared to the engine provides a means of adjusting the pitch of the propeller blades to maintain a speed set by the pilot. In accordance with this invention, bodi propellers may be driven at the same speed through a common gearbox, thus individual propeller governors to set the speeds of the propellers is not necessary. Instead, means such as an automatic hydraulic selector valve may be provided so that engaging the gears, e.g., via gearing control arm 111 (Figure 37), will automatically select one propeller governor to control all the props, leaving the remaining propeller governor(s) as safety backups. The Mounting Armatures A particularly innovative feature of preferred aircraft according to this invention is the incorporation of pivotal mounting armatures, already discussed with reference, e.g., to Figures 1, 4, 6, 7, 34, 36 (and many of the other drawings). Further appreciation of composition and function of the pivotal mounting armatures will be gained by reference to Figures 38, 39, 41, and 42, which show starboard and port mounting armatures isolated from the body of the aircraft but in proper spatial relationship to each other, as if they were installed on an aircraft in accordance with the teachings herein. Referring to Figure 38, opposingly positioned starboard (6) and port (7) mounting armatures are shown in perspective, in the* orientation they would have in, e.g., an aircraft as pictured in Figure 5 (landing gear retracted, propeller centers level with the wings). Flotational pontoon landing gear (22 and 23) are incorporated in or mounted at one end of each mounting armature (6, 7), and a starboard caster-type stabilizing wheel (18) is shown retracted into a recesses in the starboard pontoon (22) (the like port caster-type stabilizing wheel is not visible in this view). The pivot points of each armature are indicated at P in Figure 38, and it is through the pivot points that the mounting armatures (6 and 7) are pivotally fixed to the main wing structure (1 in Figure 36) by a pivot shaft (91 in Figure 36). The propellers (8 and 9, indicated by circular arcs in Figure 38) are mounted at die opposite end of eidier armature (6, 7) from the landing gear, in nacelles (314) formed in the surface of the armatures. The belt-and- pulley drive system for the propellers, discussed previously widi reference to Figures 34, 35 and 36, is recalled in this figure by the partial cog belt (99) and the pivot transfer drive shaft (291). The propeller drive belt (84 in Figure 36), and the propeller drive pulley and shaft are enclosed within the mounting armature and thus are not visible in this drawing. The pivotal mounting armatures of the present invention provide a means of coordinating the placement of die propellers and the exposure of different types of landing gear. It will be appreciated by reference to drawings such as Figure 38 that the compound landing gear mounted at the lower ends of the armatures are kept at substantially the same distance from the propellers mounted on the upper ends of the armatures. But while the separation of landing gear and propellers remains constant, their orientation with respect to the rest of the aircraft (and the ground) may be changed, because of the pivotal attachment of the armatures to the fixed wing structure (1 in Figure 1) of the aircraft. Referring to Figure 39, the armatures (6 and 7) may be considered as having an upper end (or propeller end) and a lower end (or landing gear end) with respect to the pivot points (P). For example, the upper end of armature 7 in Figure 39 is indicated by the arrowed line U-U, and die lower end of the armature 7 is indicated by die arrowed line L-L. While not wishing to be limited to one particular shape or any particular set of concrete dimensions, the preferred mounting armatures depicted in the drawings may be broadly described as incorporating four segments, at differing angles to one another, indicated as W, X, Y, and Z in Figure 39. A dashed line represents a centerline through all four segments of mounting armature 7. It will be appreciated that segments W and Y are substantially perpendicular to each odier, since, in die orientation illustrated here, segment W is coextensive with the wing structure and segment Y is coextensive with die fuselage. The relative angle of segment X, which connects segments W and Y, may vary widely according to design choices but ideally is sufficient to accommodate the angle of a single drive belt (e.g., 99 in Figure 35) extending from the inboard engine shaft (172 or 173 in Figure 34) to die transfer pulleys on the pivot shafts (e.g., 291 in Figure 35). The angle of segment Z, which extends inboard from segme /nt Y, also may vary widely in accordance with design choice but ideally is sufficient to conform the angle of the segment Z to the angle of the keel of the hull-type fuselage (300 in Figure 35). The barrier dimensions of the armatures will generally follow the centerline but may taper and curve in order to provide fairing, to improve d e fit of the armature into recesses, or to make the outer surfaces of the armatures aerodynamically smooth or capable of merging with an aerodynamic surface (i.e., wing or fuselage). Referring again to Figure 39, the precise dimensions of die segments W, X, Y and Z may vary, so long as at least one object of the invention is accomplished. Segment W must be long enough to prevent the propeller blades (8 and 9) from striking the fuselage at all points of rotation of the armatures and must not be so long that at the armatures' farthest rotation away from the fuselage (see, e.g., Figure 9) the propellers (8 and 9) mounted in the upper end (U-U) physically interfere with each other. (Slight overlap of the propeller arcs may be accommodated, however, by fore-and-aft staggering of the propellers.) The dimensions of segments X, Y and Z together cannot be so long that the lower end (L-L) of the armature (i.e.. the pontoons 22 and 23) fail to clear the water during a water landing. That is, at maximum rotation of the armatures away from the fuselage (see, e.g., Figure 9), the pontoons (22 and 23) must be above the water line of the fuselage. It will be additionally appreciated, referring briefly to Figures 6-10, that the mounting armatures (6 and 7) are shaped such diat deployment of the stabilizing landing gear to any of the landing positions places the lower end of the armatures outboard of the pivot point, and therefore the forces encountered on landing tend to open rather than to collapse the armatures and landing gear. In accordance with these factors, in an aircraft according to this invention having the dimensions recited supra for a most preferred embodiment having die general configuration illustrated in Figure 1 (see page 13), by way of illustration and not of limitation, the dimensions of the mounting armatures would be as follows: Segment W, 44-48 in. (1.12-1.22 m); segment X, 19-24 in. (0.48-0.61 m); segment Y, 34-38 in. (0.86-0.965 m); segment Z, 28-32 in. (0.71-0.81 m); angle α (between W and X), 145° to 155°; angle β (between X and Y), 115° to 125°; and angle γ (between Y and Z), 110° to 130°. The most preferable dimensions for this particular embodiment: W, 46 in. (1.17 m); X, 21.5 in. (0.546 m); Y, 36 in. (0.91 m); Z, 30-31 in. (0.77 m); α, 150°; β, 120°; γ, 120°. Referring to Figure 40, a cross-section of the starboard wing (ref. Figure 3) is shown, where the mounting armature (6) is rotated fully inboard, so that the upper end of the mounting armature has merged with the fixed wing structure (1). Figure 40 shows a smooth aerodynamic surface provided by the now juxtaposed wing structure (1) and mounting armature (6). Within the armature housing, the propeller shaft (81) is seen to extend from the starboard propeller (8) through a bearing (82) in the rear upper armature spar (71) to a bearing (82) in the forward upper armature spar (70). The split flap (72) of the fixed wing section (1) is shown in raised position, and the leading edge slat of the main wing section (1) is shown fully retracted. Referring to Figure 41, the two pivotal mounting armatures (6 and 7) are shown as in Figure 38, except diat bodi armatures have been rotated around the pivot points (P) to be in the appropriate orientation for landing on a hard surface or runway. Rotation of the armatures to the position illustrated brings the stabilizing wheels (18) into position for landing. The wheels are swung out from the recesses in the pontoons (22 and 23, ref. Fig. 38), e.g., by means of an actuating lever linked to one segment of a multilink actuating strut (not shown, discussed infra). The propellers (8 and 9), in this orientation, are raised far enough above the wing so that substantially all of the arc of each propeller is above the wing. This is advantageous for takeoff and landing attempts, because the propeller blades in raised position are less likely to encounter debris from the ground and the propeller wash is directed over the control surfaces of the tail section. Referring to Figure 42, the two pivotal mounting armatures (6 and 7) are shown as in Figure 38, except that bodi armatures have been rotated around the pivot points (P) to be in the appropriate orientation for landing on water, i.e., the pontoons (22 and 23) have been rotated into the appropriate position, die stabilizing wheels (18) have been retracted, and die propellers (8 and 9) have been raised to their maximum distance above the wing. In this orientation, the propellers are shielded by the wing from water spray, and the prop wash is conducted more directly over the control surfaces of the tail section. The increased downward lift caused by the prop wash over the tail section partially counteracts the undesirable forward (nose-down) pitch diat results from raising the thrust line. It should be recalled, however, that even though the thrust line is raised by rotation of the armatures, the center of gravity does not change appreciably, since the mass of the engines remains below the wings, in the fuselage. Referring to Figure 43, a cross-section of the starboard wing (ref. Figure 1) is shown, where the mounting armature (6) is rotated partially outboard, so that the upper end of the mounting armature is raised above the fixed wing structure (1). Within the armature housing, the propeller shaft (81) is seen to extend from the starboard propeller (8), through a bearing (82) in die propeller nacelle bulkhead (112), dirough anodier bearing (82) in die rear upper armature spar (71), to a bearing (82) in the forward upper armature spar (70). A propeller drive pulley (83) is attached to die propeller shaft (81) and is turned by a propeller drive belt (84), which extends down to a pivot transfer drive pulley (unnumbered) attached to a pivot transfer drive shaft (291). A transfer pulley (94) also attached to the pivot transfer drive shaft (291) is turned by a drive belt (99). The split flap (72) of the fixed wing section (1) is shown in a lowered position, and the leading edge slat (14) of the main wing section (1) is shown fully extended. The mounting armatures of the present invention may be actuated by any conventional means diat serve to rotate the armatures about ieir pivot mounts. Pressure-driven (e.g., hydraulic, air) or screw-driven rods, for instance, that are set transversely in die fuselage and are extended horizontally to push the lower ends of the armatures away from the fuselage may by utilized, or gear-driven pivots (P in Fig. 42) may also be employed. These mechanisms, however, have disadvantages relating to the precision with which the armature extension can be controlled and relating to the absorption of landing stresses. The preferred actuator mechanism for extending and retracting the pivotally mounted armatures according to this invention is a multilink actuator strut such as is depicted in several of the frontal elevation drawings discussed previously. (See, for example, items 280 and 281 in Figures 6, 7, 8, 9 and 10.) Referring first to Figure 9, in which die multilink actuator struts (280 and 281) are at their fullest extension, the struts are seen to form (with die fuselage and the armatures) an arrangement of two back-to-back 4-bar linkages. For each multilink actuator strut, a series of four rectangular links, connected end-to- end and togedier measuring the proper length to achieve the maximum desired outboard rotation of the mounting armatures, is attached at one end to the fuselage and at the other end to the lower end of the mounting armature. These connections leave iree joints in the series of four links between the fuselage and the mounting armature. A fifth link is attached at one end to the center joint in the 4-link series and is attached at the other end high on the fuselage, so that the fifth link, the fuselage and the inboard two links of the 4-link series form a 4-bar linkage. Two hydraulic (pictured) or screw-driven actuators are connected to the 4-link series so as to permit collapse (independently) of the outboard two links and the inboard two links at the unbraced joints. By collapsing the inboard two links, an intermediate positioning of the armatures is achieved (see, Figures 6, 7 and 8); and by collapsing botii the inboard two links then the outboard two links, the entire 4-link series is folded into the fuselage (see, e.g., 280 and 281 in Figure 35), and the armatures are fully retracted. The links of the multilink actuator struts will be sized to provide the exact positioning of the armatures necessary to deploy the desired configuration of landing gear or propeller position. Collapse of one or both of the 4-bar linkages of the multilink actuator struts will provide automatic "stops" to the mounting armature rotation, eliminating the need to calibrate the pressure or screw-driven components of the actuator system. The Compound Landing Gear A further innovative feature of preferred aircraft according to the invention is the incorporation of compound landing gear that enable the aircraft to be modified in flight for landings on a variety of surfaces (water, hard surface, snow). Prior to this invention, there were no aircraft capable of safe landings and takeoffs from all of water, tarmac and snow, and certainly no aircraft that could be modified to land on any of those surfaces, at the option of the pilot, while still in flight. Aircraft incorporating the compound landing gear described herein will not only have the capability of landing on many surfaces, they will realize additional advantages from the particular design of die compound landing gear. For example, die compound landing gear of the present invention is expected to provide more efficient transmission of the inertial load to the ground on hard landings. In addition, the utilization of ski-type gear that may be retracted to be substantially flush with the fuselage is expected to provide a shock-absorbing effect in die event of a "wheels-up" landing (belly landing). Also, having die primary landing gear descend from the fuselage requires shorter landing gear mounts (compared with wing-mounted landing gear) which have a lower bending moment and are thus less apt to collapse from incidental lateral loads, such as from tight radius turns at too high a speed, landings with incorrect drift correction, or even collisions with ground vehicles. The compound aircraft landing gear of the present invention include three components: A) a forward landing gear component positioned forward of the center of gravity of the aircraft, substantially completely retractable into the fuselage, including integrated steerable ski and steerable wheel subcomponents; B) a main central landing gear component, substantially completely retractable into the fuselage, including integrated skis and steerable wheel subcomponents, each of which may be deployed to a point 8-13° (preferably 10-11 °) aft of the center of gravity of the level aircraft and which, when retracted, assist in formation of (or retract to form) a step in the fuselage at a point 8-13° (preferably 10-11 °) aft of the center of gravity of the level aircraft; and C) a lateral stabilizing gear component comprising two bilaterally situated stabilizing members, each of which may be deployed on eidier side of the aircraft to a point 8-13° (preferably 10-11 °) aft of the center of gravity of the level aircraft and substantially aligned with the main central landing gear, and each member including integrated pontoon and wheel subcomponents. The subcomponents of each component of the compound landing gear will be mounted in such a way that each of all die wheel subcomponents, or all the ski subcomponents, or all the pontoon subcomponents will be separately deployable to act as the primary landing gear for the aircraft, that is, deployable to a position where the wheels, or the skis, or the pontoons become the lowest points of the level aircraft with respect to the ground (i.e., the points of contact with the ground during a landing operation). Preferably, the forward and main central landing gear will be mounted in such a way diat when fully retracted die ski-type gear will nestle into the fuselage opening dirough which the gear are deployed, and the bottoms of the skis will be substantially flush with die outer surface of the fuselage, thereby eliminating die need for enclosing nose and gear bay doors. (See, Figure 44, position of skis 29; Figure 50, position of skis 147.) Most preferably the subcomponents of each landing gear component will be integrated in such a way diat, wherever possible, full deployment of one subcomponent will automatically prevent full deployment of another subcomponent, so diat no two sets of landing gear may be inadvertently deployed to their fullest extent and become, collectively, die primary (lowest deployed) landing gear for the aircraft. The most preferred embodiments will, however, permit coordinated action of the subcomponents where it is advantageous, for example, in providing ski-type landing gear that can be raised to a level just slightly above the lowest point of the tires of the wheel gear, which is the best configuration for landings on intermittent snow- covered and clear hard surfaces. (See, Figures 46 and 57.) As described below and with reference to the drawings, aircraft incorporating the compound landing gear of this invention are uniquely serviceable and safe. Figures 44, 45, 46, 47, 48 and 49 illustrate the deployment and operation of a preferred forward landing gear component of a compound landing gear according to die invention. The same structural members are shown in each of these figures at different stages of deployment. The reference numbers for each of the members are the same from figure to figure. Referring to Figure 44, a forward landing gear assembly is shown having the essential forward landing gear component functionalities, namely, full retractability within the fuselage (300) of the aircraft, separate deployability of either wheel or ski subcomponents, and steerability of the skis and wheels once deployed. As illustrated, die forward landing gear component is comprised of members for positioning (i.e., deploying or retracting) the wheel gear and ski gear, members for actuating the positioning of the gear relative to the aircraft, members for positioning the ski gear subcomponent relative to the wheel subcomponent, and (preferably) members for absorbing landing forces (i.e., one or more shock absorbers or springs). The actual steering mechainism has been omitted for the sake of clarity. Also, a braking mechanism will typically be included but is not illustrated here for the sake of clarity. Referring again to Figure 44, the subcomponents of the forward landing gear are embodied in a steerable wheel (21) (or, alternatively, two steerable wheels), preferably having a pneumatic tire, and two skis (29, port ski only is shown), connected to the front wheel axle (208) by a front ski actuator link (204), which connects to each ski at a pivotal mount (209). The wheel (21) of course turns freely on its axle (208), but the ski pivotal mounts (209) have stops (not shown) that will limit the arc that can be described by die skis, to prevent the skis from rotating so far forward or backward that the aircraft can nose into the snow or bottom out, during a snow landing. The axle (208) of the front wheel (21) is connected by a tubular steering column (316) (or shaft) to a steering control plate (193). A swing-out mounting cylinder (230) acts as a housing for the steering column (316), within which the column is freely rotatable by actuation of the steering control plate (193). The actual steering mechanism, through which the steering control plate (193) is turned, is not shown here, but preferably die steering mechanism (e.g., steering cables or similar mechanism (ref. Fig. 60)) is attached to the steering control plate (193) in such a way that the control plate (193), and therefore the front wheel (21) and skis (29), become steerable only when they are lowered for landing: That is, the steering column (316) can be rotated wid in the swing-out mounting cylinder (230) only when die mounting cylinder (230) is swung-out to an approximately vertical orientation with respect to the aircraft. When the swing-out mounting cylinder (230) is rotated to a substantially horizontal position with respect to the aircraft, as shown in Figure 44, the steering mechanism, preferably, will not be able to actuate the steering control plate (193) or otherwise cause the forward landing gear (28, 29) to swivel. A ski deployment actuator (205) is pivotally attached at one end (206) to the steering control plate (193), and pivotally attached at its other end (207 in Figure 45) to the front ski actuator link (204). With tiiese attachments and links, die front ski actuator (205) will turn with the steering control plate (193), wheel (21) and skis (29); furthermore, the actuator (205) at this position allows the differential deployment of either the wheel gear (21) or the ski gear (29), as shown in Figures 48 and 49. The front ski actuator (205), as well as the other actuators in the landing gear assemblies, may be powered by any suitable means, depending on manufacturer's preference. Hydraulic cylinders, air cylinders, electric screw jacks and even hand cranks are all known for this sort of mechanical task. It will also be appreciated that although die foregoing description discusses single links and actuating arms, certain of the members described may advantageously be installed in pairs. For instance, it is mentioned that two skis (29) are typically (and preferably) employed in the forward landing gear component; and accordingly two actuator links (204) may be employed (instead of a single, U-shaped actuator link connecting both skis and pivotally mounted around the front wheel axle (208)), which, in turn, would necessitate dual front ski actuators (205). The forward landing gear (21, 29) and associated links and steering assemblies described previously and as mounted in the swing-out mounting cylinder (230) are connected to the fuselage (300) via a front gear suspension link (190) and a front gear connecting link (197) that is further pivotally connected to a front gear actuator link (198). The suspension link is pivotally attached to die fuselage (300) at one end (191) and pivotally attached at its other end (194) to the upper end of die swing-out mounting cylinder (230). The mounting cylinder (230) has a fin-like mounting appendage (317) projecting generally perpendicularly from the cylindrical housing for the tubular steering column (316), extending directly aft when the mounting cylinder is in an upright (vertical) orientation. The front gear connecting link (197) is pivotally attached at one end (195) to the swing-out mounting cylinder (230) at a pivot on this mounting appendage (317) and pivotally attached at its other end (200) to the front gear actuator link (198), which, in turn, is pivotally attached to the fuselage at a pivot (199). The front gear actuator link (198) also provides a pivot attachment (203) for a front gear actuator (201), which is pivotally attached to the fuselage at its other end (202). The mounting appendage (317) also provides a pivotal mounting point (196) for a shock absorber or spring (189), which is pivotally attached at its otiier end (192) to the fuselage (300). By reference to the foregoing description and die drawings (Figures 44-49), it will be appreciated that actuation of the aforementioned series of linkages causes the swing-out mounting cylinder (230) to rotate generally in the sagittal plane of the aircraft (i.e., the plane including die centerline and dividing the aircraft into symmetric halves), thus deploying or retracting the forward landing gear (wheel (21) and skis (29)). Furthermore, shortening of the front ski actuator(s) (205) deploys die skis (29) over the front wheel (21) (see, Figure 49). During extension and retraction, the shock absorber /spring (189) remains at its full length, since it does not support any of the weight of the aircraft. (See, Figures 44, 45 and 46.) In touching down for a landing (Figure 47) and while operating on the ground (Figures 48 and 49), the front gear actuator (201) remains at its fully extended length, and the front gear actuator link (198) does not rotate, so that die connecting link (197) holds its position, and the shock absorber /spring (189) compresses and decompresses as the landing or taxiing load varies. To position the skis (29) for operation on a snow-covered surface, the front ski actuator (205) is extended, which rotates the front ski actuator link (204) about the front wheel axle (208). (See, Figures 48 and 49.) On surfaces completely covered with snow it is desirable to position the skis (29) below the wheel (21) to eliminate drag from snow accumulating in front of the wheels, however during operation on surfaces where snow only partially covers the ground it is desirable to position die skis so that the tires of the wheel (21) extend slightly below the skis (29), so diat die aircraft rides up on the tires where there is no snow but rides on the skis (witii die wheels providing minimum drag) where the snow covers the ground. In order to raise or lower die skis (29) this small amount relative to the wheel (21), the front ski actuator (205) is retracted slightly from its full extension, which rotates the support (204) and lowers the skis (29) slightly. Figures 50, 51, 52, 53, 54, 55, 56, 58, 57 and 59 illustrate the deployment and operation of a preferred main central landing gear component of a compound landing gear according to die invention. The same structural members are shown in each of diese figures at different stages of deployment. The reference number for each member is the same from figure to figure. Referring to Figure 51, a main central landing gear assembly is shown having die essential main central landing gear component functionalities, namely, full retractability within the fuselage (300) of the aircraft and retractability to form a step in the hull (necessary to permit takeoff from water), separate deployability of either wheel or ski subcomponents, and steerability of the wheels once deployed. As illustrated, the main central landing gear component is comprised of members for positioning (i.e., deploying or retracting) the wheel gear and ski gear, members for actuating the positioning of the gear relative to the aircraft, members for positioning die ski gear subcomponent relative to the wheel subcomponent, and (preferably) members for absorbing landing forces (i.e., one or more shock absorbers or springs). The actual steering mechanism has been omitted for the sake of clarity. Also, a braking mechanism will typically be included but is not illustrated here for the sake of clarity. Referring to Figure 50, a sectional side elevation of die midsection of an aircraft according to die invention is shown, illustrating the general positioning, within the fuselage (300) and fixed wing section (1), of die major systems and structures, e.g., a wing extension panel (4) and associated structures (unnumbered), the engines (in silhouette, 25 and 24 (partial)), the lower end of a port pivotal mounting armature (7) including a pontoon section (23). The approximate position of the aft-most passenger within the aircraft is represented by die seated human figure (unnumbered). Figure 50 shows the position that die main skis (147) occupy in the fuselage (300), and shows die position that the armature (7) and pontoon (23) occupy in the fuselage, when the aircraft is configured for cruising flight. (Cf. Figures 3 and 9.) Full retraction of the main central landing gear and of the mounting armatures brings the main skis (147), a main wheel hatch (148) and die pontoons (23) of die mounting armatures into alignment, flush with the fuselage (300), creating a smootii outer surface. In the preferred embodiment illustrated, it will be noted diat complete retraction of the skis (147) brings the nose of die skis up into die fuselage (300), forming a slight notch or mini-step (arrow) in the fuselage, below the water line. Advantageously, tiiis notch helps to ventilate the hull when die aircraft is on the water, and it helps reduce the suction of die water diat must be overcome in order to take off from the water. Referring to Figure 51, the same view of the aircraft's midsection as in Figure 50 is shown, except that the outermost sections of the fuselage (300), as well as the main skis (147), die main wheel hatch (148), and the fully retracted mounting armature (7) and pontoon (23), have been rendered transparent, and except for the fuselage (300) these components are represented by broken lines ( . . ). The lower line of the fuselage (300) is shown by a dotted line (....) where it is covered by the pontoon (23). The main central landing gear component as illustrated in Figure 51 is comprised of one or two (preferably two, as pictured, e.g., in Figure 52) wheels (20) with (preferably) pneumatic tires, two skis (147), one or more shock absorbers or spring suspension members (129), one or more powered actuators (hydraulic or air cylinders, or electric screw jacks, or similar apparatus) (141), and various connecting and supporting members. The main wheels (20) are rotatably mounted on a central axle assembly (210 in Figure 54), to which is attached a brake system (not shown). The axle assembly (210) is connected via a steering column (not shown) to a main gear steering control plate (220) pivotally housed in a swing-out main gear mounting cylinder (133), in a similar manner to the front landing gear assembly (see, Figures 44-49). The main gear mounting cylinder (133) is also equipped with a rearward-extending fin-like mounting appendage (318) fixed to the main gear mounting cylinder (133), to which a main gear connecting link (137), a main gear suspension link (130) and (preferably dual) shock absorbers/springs (129) can be pivotally attached, i.e., at pivot connections 135, 134, and 136 (Fig. 51), respectively. As in the forward landing gear component illustrated in Figures 44-49, the steering mechanism (not shown) for the main central landing gear wheels (20) will be connected to die steering control plate (220) so that die mechanism is engaged only when the swing-out main gear mounting cylinder (133) approaches a vertical (deployed) orientation with respect to the centerline of the aircraft. The main gear suspension link (130) is pivotally attached to die fuselage (300) at a pivot connection (131). The shock absorbers/springs (129) are pivotally attached to die fuselage (300) at a pivot connection (132). The main gear connecting link (137) as illustrated in Figure 51 is a tuning fork-shaped member which extends forward from its pivot connection (135) on die mounting appendage (318) to a main gear actuating link (138), where it is pivotally attached at a pivot connection (140). The main gear actuating link (138) is pivotally attached to die fuselage (300) at a pivot connection (139). A main gear actuator (141) is also attached to die main gear actuating link (138) at a pivot connection (143) and is pivotally attached at its opposite end to the fuselage (300) at a pivot connection (142). It will be appreciated diat actuation of the aforementioned series of linkages causes the swing-out main gear mounting cylinder (133) to rotate generally in die sagittal plane of die aircraft (similarly to die mounting cylinder (230) of die forward landing gear component, described supra), thus deploying or retracting the main wheels (20). See, e.g., Figure 54, which shows the main wheels (20) and die associated main central gear structures fully deployed. During extension and retraction, the shock absorbers/springs (129) remain at full length, since they do not support any of the weight of die aircraft. In touching down for a landing and while operating on die ground (Figures 54 and 55), die main gear actuator (141) remains at a fixed extension, and die main gear actuating link (138) does not rotate, so that the main gear connecting link (137) holds its position, and the shock absorbers/springs (129) compress and decompress as the landing or taxiing load varies. The shock absorbers/springs (129) operate in the same manner to absorb landing/taxiing loads during snow landings, because the main skis (147), as more fully described infra, are connected to the same main gear connecting link (137). This latter fact leads to a further safety advantage of aircraft employing the compound landing gear disclosed herein: As can be seen witii reference to Figures 50 and 51, the main skis (147) are the lowest part of the fuselage when in the fully retracted position; however, even in the retracted position, die arrangement of the landing gear connecting and actuating structures described above permits forces applied to the skis to be transmitted to the shock absorbers/springs (129). Therefore, for water landings but more importantly for "wheels-up" landings on a hard surface (i.e., where die pilot eitiier cannot or forgets to deploy landing gear), the portion of the fuselage to come in first contact with die ground is advantageously constructed to take more punishment than the rigid fuselage of conventional aircraft. This feature, accordingly, not only improves the safety of the aircraft from the passengers' standpoint but improves the likelihood diat the aircraft will suffer minimal structural damage and will not be totally lost after this type of landing. The skis (147) of the main central landing gear component are mounted on die main gear connecting link (137) via forward and rear ski support arms (144 and 145) and main ski connecting arms (149). Referring to Figures 52 and 53, where these elements are more clearly seen, the forward and rear ski support arms (144 and 145, respectively) are pivotally attached to the main gear connecting link (137) in stepped recesses of the forward end of die member. These stepped recesses permit the ski support arms (144 and 145) to fold flat against the base of the main gear connecting link (137), when the skis (147) are in a fully retracted position as shown in Figure 52. The forward ski support arms (144) are generally triangular in shape, with two pivotal connections (213 and 214 in Figure 53) along the base to the main gear connecting link (137), and a biaxial pivot connection (150) at the apex to the main ski connecting armg (149). As best illustrated in Figure 53, each rear ski support arm (145) is generally rectangular in shape (ref. Figure 57) and has pivot connections to die main gear connecting link (137) at one end and a pivotal connection at the opposite end to a V-shaped double axle member (238), dirough which each rear ski support arm (145) is connected to a main ski connecting arm (149). One arm of the V-shaped double axle member (238) is pivotally attached to die rear ski support arm (145); the otiier arm of die V-shaped double axle member (238) extends dirough the main ski connecting arm (149) and forms a pivot connection (150) about which the main ski connecting arm (149) pivots. The relative angle of the arms of die V-shaped double axle member (238) is such that the lower surface of the skis (147) are caused to be horizontal to the ground when die assembly is fully deployed and are caused to substantially match the angle of the fuselage when the assembly is fully retracted. The base of each main ski connecting arm (149) is pivotally attached to a ski (147) by pivot connections (152) to flanges on the upper surface of the ski (147), as shown in Figure 53. Also shown in Figure 53 are screw-driven ski positioning actuators (215 and 216) for extending the skis (147) from tiieir fully retracted position (see, Figure 52). The rear ski support arm actuator (215), which is pivotally attached to the support arm as shown (239), pushes the rear ski support arm (145) away from the main gear connecting link (137), which forces the skis (147) down and away from the fuselage. Extension of the forward ski support arm actuator (216), pushes the upper corner of the forward ski support arm (144) away from the main gear connecting link (137), thereby lowering the biaxial pivot connection (150) and causing die position of the main ski connecting arm (149), and dius the main skis (147), to change by rotation about the pivot connection (151) to die V- shaped double axle member (238). It will be appreciated by reference to the foregoing description and die drawings (esp. Figures 51, 52, 53, 55, 57 and 58) diat by coordinated extension and retraction of the ski positioning actuators (215 and 216), the main skis (147) can be raised and lowered through a wide range of positions relative to the fuselage. Although not critical to the invention, the various members comprising the main central landing gear component may be shaped and constructed to provide additional flotation elements, lending an additional feature to the multifunctional landing gear component. As pictured in Figure 52, for instance, the main ski connecting arm (149), rather than being fabricated as a solid shaft or bar, has been shaped to fill the space between die fully retracted skis (147) and the flat-folded forward and rear ski support arms (144 and 145). Thus shaped, the main ski connecting arm (149) may be fabricated (without compromising its structural strengtii) to be hollow, with the hollow compartment being watertight or filled witii a buoyant foam. The main ski connecting link (137) pictured in Figure 52 may likewise be fabricated witii hollow compartments for buoyancy. The bay in the fuselage which houses the main central landing gear component preferably will not be designed to be watertight, since this would significantly complicate the design and sharply raise construction costs. Accordingly, when die aircraft is on the water, the bay will be exposed to water, and any additional flotation elements such as the buoyant connecting arm (149) will improve the seaworthiness of die aircraft. Referring briefly to Figure 55, a cross-sectional side elevation of die midsection of an aircraft equipped witii die preferred main central landing gear component of this invention is shown, and die landing gear are deployed for a snow landing. To position die skis for operations on snow-covered surfaces, the rear ski support arm positioning actuator (215 in Figure 53) is extended, which rotates the forward and rear ski support arms (144 and 145) out from the main gear connecting link (137). The ski support arms (144 and 145) position d e main ski connecting arms (149) so that die pivot line (152) of the skis (147) is near that of die main wheels (20). Adjustment of the level of the skis using the forward ski support arm positioning actuator (216 in Figure 53) permits configuration of the main central landing gear for proper balance of the aircraft on all types of snow-covered surfaces, in particular during lift-off and touch-down. On totally snow covered surfaces it is desirable to position the skis (147) below die wheels (20) to eliminate drag from snow accumulating in front of the wheels. (See, e.g., Figure 58.) During operation on surfaces of intermittent snow and clear surface, the skis are advantageously positioned so that the bottoms of the wheels (20) extend slightly below the skis (147) and the aircraft consequently rides up on die tires where there is no snow but rides on the skis (with die wheels providing minimum drag) where the snow covers the ground. (See, e.g., Figure 57.) Referring again to Figures 54 and 55, it is important to note that the main central landing gear component is positioned almost directly underneath the engines (24 and 25). In a twin-engine aircraft, about half of the total weight of the aircraft is accounted for by the engines. In conventional propeller aircraft, that load (i.e., the mass of die engines) is out on the wing structures; in aircraft as illustrated in Figures 54 and 55, die load is mounted inboard, directly over the landing gear. In a hard landing, the energy of the mass of die engines coming into contact with the ground is dissipated through the landing gear; and in conventional propeller aircraft that energy is translated through the wings to the fuselage and to the landing gear, putting a lot of stress on the wing structure. With an arrangement of engines and landing gear as illustrated in Figures 54 and 55, the energy of the mass of the engines at the velocity of a hard (as opposed to a soft) landing is dissipated directly to the main central landing gear component through die bottom of the fuselage, without putting those stresses on the wings or other structures of the fuselage. This is anodier feature which makes aircraft according to this invention more forgiving of common pilot errors. Figures 56, 58, 57, and 59 further illustrate the deployment and operation of a lateral stabilizing gear component of compound landing gear according to the present invention, comprising bilaterally situated stabilizing members, including integrated wheel and pontoon subcomponents. The drawings show a particularly preferred embodiment, wherein the stabilizing gear are integrated in pivotal mounting armatures also according to die invention. It will be recognized diat less preferred embodiments of the stabilizing gear component may alternatively be mounted under the wings or extended from die fuselage on separate supporting members. Employing the mounting armatures gives the stabilizing gear the added advantage of being fully retractable, as well as being coordinated with the position of die propellers. Figures 56-59 present similar frontal elevations of an aircraft according to die invention, showing die relative orientation of the main central landing gear component and the lateral stabilizing gear component, in each of four landing configurations. Previously discussed elements such as the propellers (8, 9), engines (24), belts, flaps (72), ailerons (10, 11), main skis (147), main wheels (20), etc. are provided for reference, however many previously discussed structures have been omitted from these views for the sake of clarity. As illustrated in the embodiment of Figure 56, the pontoons (22 and 23) are integrally mounted on, and form the lower segment of, die pivotal mounting armatures (6 and 7, respectively). Thus, rotation of the armatures away from or into the fuselage (300) by means of the multilink actuating struts (280 and 281) deploys or retracts the pontoons (22 and 23). Stabilizing wheels (18 and 19) are attached to the pontoons (22 and 23) by wheel mounts of course permitting free rotation of the stabilizing wheels. The wheel mounts may be fixed or (preferably) retractable. In the embodiment illustrated, the pontoons are fabricated with recesses into which the stabilizing wheels (18 and 19) can be retracted. Extension or retraction of the stabilizing wheels (18 and 19) may be performed by any suitable means (e.g., separate powered actuators); however, preferably the stabilizing wheels (18 and 19) are mounted, as shown here, so as to automatically extend or retract according to die rotation of the pivoting mounting armatures (6 and 7), which is effected by means of starboard and port stabilizer actuating links (168 and 169, respectively) fixedly attached at one end to the respective starboard and port multilink actuating struts (280, 281), and pivotally attached at the other end to pivotal wheel mounts to which the stabilizing wheels (18 and 19) are rotatably mounted. The stabilizer actuating links (168 and 169) are fixedly attached to the final (outboard-most) link of the 4-link series of each multilink actuating strut (280 and 281; ref. description, supra), so that at intermediate extension of the multilink actuating struts (280 and 281), retractable wheel mounts are forced down, swinging the stabilizer wheels (18 and 19) into a deployed position. (See, Figures 56, 58, 57.) When the 4-link series of the multilink actuating struts are at full extension (Figure 59) or when the outboard 4-bar linkage is collapsed (i.e., when the mounting armatures are retracted to die fuselage), the angle of the final link of the multilink actuating struts (280 and 281) changes, and the stabilizer actuating links (168 and 169) are pulled upwards, causing die stabilizing wheels (18 and 19) to swing back into tiieir respective recesses in the pontoons (22 and 23). The stabilizer wheels are preferably non-steerable and are on caster mounts, so that they swivel to roll in any direction that die aircraft takes, as soon as they are in contact with the ground. Each of the subcomponents of the main central landing gear and the lateral stabilizing gear (i.e., main wheels, stabilizer wheel, main skis, pontoons) must be mounted in the aircraft so that when fully deployed, the center or pivot axis of the subcomponent (e.g., hub of the wheel or pivot mount of the ski) is positioned at a point 8-13°, preferably 10-11 °, aft of the →9- center of gravity of the level aircraft. Furthermore, when the lateral pontoon members are deployed (22 and 23 in Figure 59), the exposed underside of the fuselage (see, dotted line in Figure 51) must form a step 8-13°, preferably 10-11 °, aft of the center of gravity of the level aircraft. By "level aircraft" is meant an aircraft where the fuselage is level fore-and-aft with respect to level ground, i.e., the longitudinal axis of the aircraft is parallel to the ground. A plumb line from the center of gravity of a level aircraft will be perpendicular to the centerline; and the center of each aft landing gear subcomponent, when fully deployed, must be far enough aft of the center of gravity so that a first line, extending from the center of the deployed landing gear subcomponent (e.g., the hub of the main or stabilizing wheel), parallel to the longitudinal axis of the aircraft that includes the center of gravity, to intersect the transverse axis of the aircraft that includes the center of gravity, and a second line that is a plumb line from that point of intersection of the first line and the transverse axis will form an angle of 8-13° and preferably 10-11 °. If the landing gear design caused the landing gear to be deployed forward of the first line, the aircraft would be prone to rotating back on its tail and never allowing the nose gear to touch down. If the landing gear design caused the landing gear to be deployed too far aft of the first line, the rotational force coming down on die nose gear during landing would be too great for the forward landing gear (and possibly die nose section of the fuselage) to handle without damage. If a step in the fuselage is placed too far back, the drag of the water on the fuselage will be too great to overcome, and the aircraft will not be able to take off from water. Figures 60 and 61 diagram two possible steering mechanisms for die steerable forward landing gear and the steerable main central landing gear. In the mechanism of Figure 60, the main central landing gear and die forward (nose) landing gear are steered by the same mechanism, with die nose gear additionally independently steerable by the rudder pedals (229; R - right, L - left). In Figure 61, the steering mechanisms for the nose gear and die main central gear are independent. The coordinated mechanism of Figure 60 is preferred. Referring to Figure 60, cable-and-pulley connections are made between a steering actuator plate (223) and the forward gear steering control plate (193; see, also, 193 in Fig. 49) and the main central gear steering control plate (220; see, also, 220 in Fig. 54). The steering actuator plate (223) is driven by the steering control motor (224), which is connected to the actuator plate (223) through a gear box (225). An override hand crank steering control (226) is preferably provided in die event that the steering control motor (224) becomes inoperative. The positioning of the steering actuator plate (223) is translated to the main central landing gear via cables (221) connecting to the main gear steering control plate (223). Pulleys (222) are provided to guide tiiese cables (221). The positioning of die steering actuator plate (223) is translated to the forward landing gear via cables (227) connecting to the forward gear steering control plate (193). Pulleys (222 and 235) are provided to guide the cables (227) appropriately. The forward gear steering cables (227) also loop around pulleys (237) rotatably fixed to d e rudder pedal connecting bar (240) in a slack-giving/slack-taking arrangement, so that movements of the rudder pedal connecting bar (240) are also translated to the forward gear steering control plate (193). Referring to Figure 61, a similar arrangement of cables and pulleys to die scheme of Figure 60 is shown, except the forward gear steering cables (227) do not connect with the steering actuator plate (223), and therefore the forward (nose) landing gear and main central landing gear steering controls are independent. With the steering mechanism design shown in Figure 61, the pilot adjusts the main central landing gear steering angle by operating the steering control motor (224) (or the override handwheel (226)) to compensate for or cancel the "crab" angle to which the aircraft is turned at takeoff or landing to compensate for cross-wind conditions, dius matching die angle of the landing gear to the direction of the runway. The pilot also sets the same angle into the nose gear using the rudder pedals (229). With the steering mechanism design shown in Figure 60, however, the pilot sets both the main central landing gear and nose gear angle with die steering control motor (224) (or handwheel (226)). The rudder pedals (229) are used only to make fine adjustments to the nose wheel with respect to the angle already set by positioning of the main central landing gear. Pilots will recognize that the incorporation of steerable forward and main central landing gear virtually eliminates the cross-wind limitation inherent in aircraft with conventional landing gear designs, especially where this fore and aft steerable landing gear feature is combined in an aircraft having the compound wing structure, described previously, which can be activated to dramatically lower the stall speed of the aircraft. Industrial Applicability A 1/5 scale model of an aircraft according to die invention was constructed out of balsa wood witii a styrofoam-filled core and a fiberglass shell. The model had the fuselage and wing configuration of an aircraft as illustrated in Figure 1, and it was powered by two 2.2- horsepower, single-cylinder model airplane engines and props, mounted on the ends of armatures (see, e.g., items 6 and 7 of Fig. 1) raised above die wings. The model was suitable for studying general flight characteristics on takeoff, landing and low speed cruising flight. Remote-controlled flight of die model indicated acceptable flight performance (including rudder effectiveness at low speed) and good correlation to predicted performance. Two computer modeling programs were written, one to predict performance and one to predict stability of an aircraft based on input of data describing the size, weight, power and configuration of components. The programs were tested and verified using published data from extensive wind tunnel studies conducted by the U. S. Air Force. A computer model of an aircraft according to the invention was then compared against a computer model of a "conventional" aircraft patterned after several known production twin-engine or amphibious aircraft. The computer comparisons predicted that the configuration of aircraft according to the invention having inboard-mounted engines reduced the power requirements by as much as 20% over those of a conventional twin-engine aircraft. Additionally, aircraft according to the invention having the engine and drive system and die extendable wing system described herein had a single engine climb rate 120% higher than that of a conventional twin-engine aircraft model. In comparison to a conventional amphibious aircraft, presuming a single engine mounted on a pylon above the fuselage, die computer model aircraft according to tiiis invention had a maximum level cruise speed of 160% that of the conventional model. Wind tunnel tests of small models of aircraft as described herein in various configurations (e.g., wings retracted, wings extended, central landing gear deployed) were conducted and showed favorable aerodynamic characteristics in all configurations. In particular, desirable non-turbulent airflow was observed across the vertical and horizontal control surfaces of the tail section when the main wing section was placed in and near the stalled attitude. Multi-purpose aircraft having a range of performance capabilities may be produced according to the foregoing description using conventional materials and well known aircraft construction techniques. The major structural components of preferred aircraft according to this invention are shown in Figure 62, which is an exploded perspective view of an aircraft similar to the embodiment illustrated in Figure 1. Most of the structural members pictured in Figure 62 may be readily and preferably fabricated out of aluminum stock, e.g., by high-pressure water jet cutting. Most of the structures illustrated in Figure 62 have already been described and will not be further described here. The reference numerals employed here correspond to the descriptions supra. Witii respect to die primary structure of the fuselage, Figure 62 illustrates the modular design of die aircraft: The primary fuselage structure is formed by bolting a main fuselage section (300) including a tail section (310) end-to-end witii a forward cabin module (233) and, optionally, witii an intermediate cabin extension module (234). An upper cockpit assembly (3) and an upper cabin extension assembly (2) are attached to the forward sections of the fuselage primary structure to provide a continuous cabin enclosure. As illustrated in Figure 4, the intermediate cabin extension module (234) and associated upper cabin assembly (2) may be omitted during construction of the aircraft to produce a shorter, lighter aircraft. Alternatively, for a larger enclosed cabin space, wide-body upper cockpit and upper cabin extension assemblies (231 and 232, respectively) may be substituted during construction for the standard upper cockpit and cabin extension assemblies (3 and 2, respectively). A wide-body version of the aircraft, illustrated in plan in Figure 63, results. Thus, several different types of aircraft may be assembled in die same plant, without redesign of the primary structural components. From the foregoing description, many different embodiments of aircraft incorporating innovative features according to this invention will be possible. All such embodiments, including obvious variations of the particularly preferred designs disclosed herein, are intended to be within the scope of tliis invention, as defined by the claims diat follow.

Claims: Claims 1. An aircraft capable of takeoff from and landing on eitiier snow or a hard surface, comprising: a wing structure; a fuselage; a forward landing gear assembly moveable relative to said fuselage during flight from a first position substantially retracted within said fuselage to a second position substantially extended from said fuselage, said forward landing gear assembly comprising a steerable forward wheel assembly and a steerable forward ski assembly, said forward landing gear assembly further comprising a forward landing gear actuator assembly operable by the aircraft's pilot during flight which selectively deploys said steerable wheel assembly or said steerable ski assembly to said extended second position for landing; a main landing gear assembly moveable relative to said fuselage during flight from a first position substantially retracted within said fuselage to a second position substantially extended from said fuselage, said main landing gear assembly comprising a main wheel gear assembly and a main ski gear assembly including a pair of skis, said main landing gear assembly further comprising a main landing gear actuator assembly operable by the aircraft's pilot during flight which selectively deploys said main wheel gear assembly or said main ski gear assembly to said extended second position for landing. 2. The aircraft of claim 1, wherein said main landing gear assembly in said first position forms an integral part of said fuselage with said main ski gear assembly forming die exterior surface thereof, said skis of said main ski gear assembly in said retracted position forming a substantially flush surface with said fuselage. 3. The aircraft of claim 1 , wherein said main landing gear actuator assembly comprises: a main gear connecting link; forward and rear ski supports carrying said main ski gear assembly pivotally attached to said main gear connecting link; forward and rear positioning actuators for pivoting said forward and rear ski supports relative to said main gear connecting link; and a main gear mounting assembly pivotable relative to said main gear connecting link, permitting said main wheel gear assembly to move from a retracted position relative to said main gear connecting link to an extended position for landing on a bard surface. 4. The aircraft of claim 1 , wherein said forward landing gear actuator assembly comprises: a positioning assembly for deploying and retracting said forward wheel assembly and said forward ski gear assembly relative to said fuselage; a ski deployment actuator for positioning the forward ski gear assembly relative to the forward wheel assembly; whereby control of the extension of said ski deployment actuator determines whedier the forward ski gear or the forward wheel assembly is in die appropriate position to contact die ground upon landing. 5. An aircraft having a landing gear assembly operable in flight for permitting the aircraft to land on a hard surface or water, comprising: a wing structure; a hull fuselage; a forward landing gear assembly moveable relative to said fuselage from an extended position for landing on a hard surface and a retracted position during flight or for water landing; a main landing gear assembly moveable relative to said fuselage during flight from a first position substantially retracted widiin said fuselage to a second position substantially extended from said fuselage, said main landing gear assembly comprising a main wheel gear assembly and an elongate planing member; said main landing gear assembly further comprising a main landing gear actuating assembly operable by the aircraft's pilot during flight which deploys said main wheel gear assembly to said extended second position for landing on a hard surface; wherein said main landing gear assembly, when in said retracted first position, forms an integral part of the fuselage, with said elongate planing member forming part of the exterior surface thereof, said elongate planing member forming a substantially flush surface with said fuselage suitable for permitting said aircraft to take off from or land on water. 6. The aircraft of claim 5, further comprising one or more propellers and a propeller drive system moveable relative to said fuselage between an upper position and a lower position, said propellers and drive system moveable by the pilot in coordination with the deployment of said main landing gear so as to position die propellers relative to die position of die landing gear. 7. The aircraft of claim 6, wherein said propeller drive system comprises: port and starboard propeller armatures pivotably mounted to said wing structure, each of said armatures having an upper end and a lower end, a port propeller mounted to said upper end of said port propeller armature and a starboard propeller mounted to said upper end of said starboard propeller armature, a port landing gear assembly mounted to said lower end of said port propeller armature comprising a port pontoon and a port wheel assembly; a starboard landing gear assembly mounted to said lower end of said starboard propeller armature comprising a starboard pontoon and a starboard wheel assembly; actuator means operable by the pilot of said aircraft during flight for selectively pivoting said port and starboard propeller armatures about their respective pivotal mounts; means for moving said port and starboard wheel assemblies relative to said port and starboard pontoons from a retracted position to an extended position substantially coplanar in a horizontal plane witii said main wheel assembly when said main wheel gear assembly is in said extended second position; said port and starboard propeller armatures being rotatable to a position such diat said port and starboard pontoons provide lateral stability for said aircraft on water and being further rotatable to a position such diat said port and starboard wheel assemblies provide lateral stability for said aircraft on a hard surface. 8. The aircraft as claimed in claim 1 or claim 5, wherein said wing structure further comprises means for extending and retracting said wing structure relative to said fuselage. 9. The aircraft as claimed in claimed in claim 1 or claim 5, wherein said aircraft comprises first and second propellers; first and second engines for driving said first and second propellers; and means for transmitting power from said first and second engines to said first and second propellers, whereby in die event of a failure in flight of eitiier of said first and second engines die remaining engine drives botii of said first and second propellers. 10. An aircraft capable of takeoff from and landing on snow, water or a hard surface, comprising: a wing structure; a hull fuselage; a forward landing gear assembly moveable relative to said fuselage during flight from a first position substantially retracted within said fuselage to a second position substantially extended from said fuselage, said forward landing gear assembly comprising a steerable forward wheel assembly and a steerable forward ski assembly, said forward landing gear assembly further comprising a forward landing gear actuator assembly operable by the aircraft's pilot during flight which selectively deploys said steerable wheel assembly or said steerable ski assembly to said extended second position for landing; a main landing gear assembly moveable relative to said fuselage during flight from a first position substantially retracted within said fuselage to a second position substantially extended from said fuselage, said main landing gear assembly comprising a main wheel gear assembly and a main ski gear assembly including a pair of skis, said main landing gear assembly further comprising a main landing gear actuator assembly operable by the aircraft's pilot during flight which selectively deploys said main wheel gear assembly or said main ski gear assembly to said extended second position for landing; wherein said forward and main landing gear assemblies, when in said retracted first position, forms an integral part of me hull fuselage, with said skis forming part of the exterior surface thereof, said skis forming a substantially flush surface with said hull fuselage suitable for permitting said aircraft to take off from or land on water. 11. A fixed wing aircraft having a plurality of propellers the positions of which relative to the fixed wing are alterable by die pilot during flight, said aircraft comprising: a fuselage; a wing structure fixedly attached to said fuselage; a propeller drive system moveable relative to said wing structure between an upper position and a lower position, said propeller drive system comprising: port and starboard propeller armatures pivotably mounted to said wing structure, each of said armatures having an upper end and a lower end, a port propeller mounted to said upper end of said port propeller armature and a starboard propeller mounted to said upper end of said starboard propeller armature, and link means operable by the aircraft's pilot during flight for pivoting said port and starboard armatures such that the upper and lower ends of said armatures alter position relative to said fixed wing structure, causing said port and starboard propellers to move between said upper and lower positions. 12. The aircraft of claim 10, further comprising first and second engines for driving said first and second propellers, and means for transmitting power from said first and second engines to said port and starboard propellers, whereby in die event of a failure in flight of either of said first and second engines die remaining engine drives both of said propellers. 13. The aircraft of claim 11 , wherein said port and starboard propellers are mounted to said upper ends of said port and starboard armatures in a counter-rotating relationship. 14. The aircraft of claim 12, wherein said first and second engines are mounted in said fuselage, in opposed relation to each other. 15. The aircraft of claim 13, wherein said means for transmitting power comprises at least two drive belts, each drive belt linking one engine to a propeller. 16. The aircraft of claim 10, further comprising moveable wing sections slidably attached to said fixed wing section, which moveable wing sections may be extended in flight to increase the wing span of said aircraft by up to 90% . 17. A multi-purpose aircraft comprising: a fuselage having a generally cylindrical structure defining a forward end and an aft end, the fuselage being closed at die forward end by a nose section and closed at the aft end by a tail section, said fuselage further having a hull-shaped underside having forward and aft landing gear openings, said fuselage further having a port lateral recess and a starboard lateral recess; a compound aircraft wing attached to said fuselage comprising (1) a fixed wing section comprising a bilaterally symmetrical aircraft wing providing lift in response to the flow of air thereacross defining leading and trailing edges and defining port and starboard halves, said fixed wing section being at least partially hollow and being open at die port and starboard ends, said fixed wing section further having a recess along the top surface of bo h the port and starboard halves; (2) a port wing extension panel comprising a forward port lift spar, a center port drag spar, and an aft port lift spar, which port spars are disposed in parallel relation and each spar being substantially the same length as said fixed wing section, substantially one-half the length of said spars being enclosed by and giving structural support to an outer skin so as to form a port aircraft wing extension section ending in a wing tip, said port wing extension section providing lift in response to the flow of air thereacross, said port wing extension panel being extendably mounted inside said fixed wing section such diat said port wing extension panel is extendable from the port opening of the fixed wing section such that substantially all of the port aircraft wing extension section protrudes from the port end of die fixed wing section and die portion of the port spars not enclosed by an outer skin being still inside said fixed wing section, said port wing extension panel further being mounted inside said fixed wing section such that said port wing extension panel is retractable within said fixed wing section such that substantially all of the port wing extension panel is enclosed by said fixed wing section; (3) a starboard wing extension panel comprising a forward starboard lift spar, a center starboard drag spar, and an aft starboard lift spar, which starboard spars are disposed in parallel relation and each spar being substantially the same length as said fixed wing section, substantially one-half the length of said spars being enclosed by and giving structural support to an outer skin so as to form a starboard aircraft wing extension section ending in a wing tip, said starboard wing extension section providing lift in response to the flow of air thereacross, said starboard wing extension panel being extendably mounted inside said fixed wing section such that said starboard wing extension panel is extendable from the starboard opening of the fixed wing section such that substantially all of the starboard aircraft wing extension section protrudes from the starboard end of the fixed wing section and die portion of the starboard spars not enclosed by an outer skin being still inside said fixed wing section, said starboard wing extension panel further being mounted inside said fixed wing section such that said starboard wing extension panel is retractable within said fixed wing section such that substantially all of the starboard wing extension panel is enclosed by said fixed wing section, said port wing extension panel and said starboard wing extension panel being mounted in such relation that said port spars and said starboard spars are in interlocking juxtaposition inside the fixed wing section so as to permit the complete retraction of both the port and starboard wing extension panels within said fixed wing section at the same time; and (4) means for effecting the extension and retraction of said port and starboard wing extension panels; one or more engines, mounted on the inside of the fuselage, each of said one or more engines, when operating, causing rotation of an engine shaft; a port mounting armature comprising a unitary body pivotally mounted on the trailing edge of the port half of die fixed wing section, the pivotal mount defining an upper portion and a lower portion of said port mounting armature, the armature being positioned on the fixed wing section and shaped so diat when pivoted to port, the lower portion of said port mounting armature nests in said port fuselage recess and the upper portion of said port mounting armature nests in the recess in the port half of the fixed wing section, the upper portion of said port mounting armature including at least one port propeller nacelle in which a port shaft and propeller assembly is rotatably mounted, which port shaft and propeller assembly extends aft of said at least one port propeller nacelle such that the propeller portion of the port shaft and propeller assembly is positioned aft of the trailing edge of the fixed wing section, said propeller portion being a pusher propeller, the lower portion of said port mounting armature further comprising integrated pontoon and wheel landing gear, said port mounting armature being further shaped such diat when pivoted to starboard, the wheel and the pontoon are oriented, at separate points of rotation of the port mounting armature, to a position 8-13 ° aft of the center of gravity of the level aircraft, and the upper portion of the port mounting armature is raised above said fixed wing section; a starboard mounting armature comprising a unitary body pivotally mounted on the trailing edge of the starboard half of the fixed wing section, the pivotal mount defining an upper portion and a lower portion of said starboard mounting armature, the armature being positioned on the fixed wing section and shaped so diat when pivoted to starboard, die lower portion of said starboard mounting armature nests in said starboard fuselage recess and the upper portion of said starboard mounting armature nests in the recess in the starboard half of die fixed wing section, the upper portion of said starboard mounting armature including at least one starboard propeller nacelle in which a starboard shaft and propeller assembly is rotatably mounted, which starboard shaft and propeller assembly extends aft of said at least one starboard propeller nacelle such that the propeller portion of the starboard shaft and propeller assembly is positioned aft of the trailing edge of the fixed wing section, said propeller portion being a pusher propeller, the lower portion of said starboard mounting armature further comprising integrated pontoon and wheel landing gear, said starboard mounting armature being further shaped such that when pivoted to port, the wheel and the pontoon are oriented, at separate points of rotation of the starboard mounting armature, to a position 8-13° aft of the center of gravity of the level aircraft, and the upper portion of the starboard mounting armature is raised above said fixed wing section; belt drive means connecting each engine shaft to at least one propeller shaft in such a manner that rotation of the engine shaft causes rotation of each propeller shaft and propeller to which said belt drive means is attached; compound landing gear comprising (1) a forward landing gear component positioned forward of the center of gravity of the aircraft, substantially completely retractable into the fuselage through said forward opening in the fuselage, including integrated steerable ski and steerable wheel subcomponents; and (2) a main central landing gear component, substantially completely retractable into the fuselage through said aft opening in die fuselage, including integrated skis and steerable wheel subcomponents, each of which may be deployed to a point 8-13° aft of the center of gravity of the level aircraft and which, when retracted, assist in formation of a step in the fuselage at a point 8-13° aft of the center of gravity of the level aircraft. 18. The aircraft according to claim 17, wherein each subcomponent of said integrated pontoon and wheel landing gear, said forward landing gear component, and said main central landing gear component, when fully deployed, is oriented at a point 10-11° aft of the center of gravity of the level aircraft. 19. The aircraft according to claim 17, wherein said port and starboard wing extension panels, when fully extended from the fixed wing section, increase the total wingspan of the aircraft up to 90-95%. 20. The aircraft according to claim 17, wherein said fixed wing section is attached to the top of said fuselage, and wherein there are twin engines tandemly mounted and opposed on the inside of said fuselage, and wherein each engine drives one shaft and propeller assembly. 21. The aircraft according to claim 20, wherein said twin engines are connected to a common gearbox which permits either engine to drive both shaft and propeller assemblies in the event of the shutdown of the other engine. 22. The aircraft according to claim 17, wherein said engines are air-cooled aircraft engines or water-cooled automobile engines. 23. The aircraft according to claim 17, wherein the fixed wing section is NACA 66 3 -018 at root and tip, has a wing chord of about 3.25 m at the root and about 2 m at the tip, dihedral of 3 degrees, sweep of -3.28 degrees at the X A chord, and a span of about 8 m; said port and starboard wing extension panels have no sweep; the wing span of the compound wing with port and starboard wing extension panels fully extended is about 15.25 m; said tail section forms a cantilever T-type tail with a span of about 4.44 m and has a horizontal stabilizer and elevator; wherein the overall aircraft length is about 12.2 m and die overall height is about 3.8 m. 24. An aircraft comprising: a fuselage having a generally cylindrical structure extending from a forward end to an aft end, being closed at die forward end by a nose section and closed at the aft end by a tail section, a fixed wing section attached to said fuselage so as to provide port and starboard wings extending laterally on either side of the fuselage, each wing including at least one propeller nacelle, each nacelle enclosing a propeller shaft rotatably mounted therein, which propeller shaft protrudes from the aft end of die nacelle and past the aft edge of the wing on which the nacelle is located, each propeller shaft having a pusher propeller fixedly attached on the shaft at a point aft of the aft edge of the wing, one or more engines, mounted on the inside of the fuselage, each of said one or more engines, when operating, causing rotation of an engine shaft, and belt drive means connecting each engine shaft to at least one propeller shaft in such a manner that rotation of the engine shaft causes rotation of each propeller shaft and die propeller to which said belt drive means is attached. 25. The aircraft according to claim 24, wherein said fixed wing section is attached to the top of said fuselage, and wherein there are twin engines tandemly mounted and opposed on die inside of said fuselage, and wherein each engine drives one propeller shaft such that the propellers are counterrotating in operation. 26. The aircraft according to claim 25, wherein said twin engines are connected to a common gearbox which permits either engine to drive both shaft and propeller assemblies in the event of die shutdown of die otiier engine. 27. The aircraft according to claim 24, wherein said engines are air-cooled aircraft engines or water-cooled automobile engines. 28. A compound aircraft wing comprising: a fixed wing section comprising a bilaterally symmetrical aircraft wing defining leading and trailing edges and defining port and starboard halves, said fixed wing section being at least partially hollow and being open at die port and starboard ends, a port wing extension panel comprising a forward port lift spar, a center port drag spar, and an aft port lift spar, which port spars are disposed in parallel relation and each spar being substantially the same length as said fixed wing section, substantially one-half the length of said spars being enclosed by and giving structural support to an outer skin so as to form a port aircraft wing extension section ending in a wing tip, said port wing extension panel being extendably mounted inside said fixed wing section such that said port wing extension panel is extendable from the port opening of the fixed wing section such that substantially all of the port aircraft wing extension section protrudes from die port end of the fixed wing section and die portion of the port spars not enclosed by an outer skin being still inside said fixed wing section, said port wing extension panel further being mounted inside said fixed wing section such diat said port wing extension panel is retractable within said fixed wing section such that substantially all of the port wing extension panel is enclosed by said fixed wing section, and a starboard wing extension panel comprising a forward starboard lift spar, a center starboard drag spar, and an aft starboard lift spar, which starboard spars are disposed in parallel relation and each spar being substantially die same length as said fixed wing section, substantially one-half the length of said spars being enclosed by and giving structural support to an outer skin so as to form a starboard aircraft wing extension section ending in a wing tip, said starboard wing extension panel being extendably mounted inside said fixed wing section such that said starboard wing extension panel is extendable from the starboard opening of die fixed wing section such that substantially all of the starboard aircraft wing extension section protrudes from the starboard end of die fixed wing section and die portion of the starboard spars not enclosed by an outer skin being still inside said fixed wing section, said starboard wing extension panel further being mounted inside said fixed wing section such diat said starboard wing extension panel is retractable within said fixed wing section such diat substantially all of the starboard wing extension panel is enclosed by said fixed wing section, said port wing extension panel and said starboard wing extension panel being mounted in such relation that said port spars and said starboard spars are in interlocking juxtaposition inside d e fixed wing section. 29. A compound wing according to claim 28, wherein the wing span of the compound wing is increased by up to 90-95%, compared to die span of the fixed wing section, when the port and starboard wing extension panels are fully extended from said fixed wing section. 30. A compound wing according to claim 28, wherein said port and starboard wing extension panels are mounted in said fixed wing section by means of rollers fastened to die inner surface of die fixed wing section. 31. A compound wing according to claim 28, wherein the fixed wing section is NACA 66 3 - 018 at root and tip, has a wing chord of about 3.25 m at the root and about 2 m at the tip, dihedral of 3 degrees, sweep of -3.28 degrees at the l A chord, and a span of about 8 m; said port and starboard wing extension panels have no sweep; the wing span of the compound wing with port and starboard wing extension panels fully extended is about 15.25 m; said tail section forms a cantilever T-type tail with a span of about 4.44 m and has a horizontal stabilizer and elevator; wherein the overall aircraft length is about 12.2 m and die overall height is about 3.8 m. 32. An aircraft comprising a fuselage having a generally cylindrical structure extending from a forward end to an aft end, being closed at d e forward end by a nose section and closed at die aft end by a tail section, a fixed wing section attached to said fuselage so as to provide port and starboard wings extending laterally on either side of die fuselage, a port mounting armature pivotally attached to the trailing edge of the port wing, the pivotal mount defining an upper portion and a lower portion of said port mounting armature, said upper portion including at least one propeller nacelle providing a mount for accepting a propeller shaft, and said lower portion incorporating a pontoon member and a wheel, and a starboard mounting armature pivotally attached to die trailing edge of the starboard wing, die pivotal mount defining an upper portion and a lower portion of said starboard mounting armature, said upper portion including at least one propeller nacelle providing a mount for accepting a propeller shaft, and said lower portion incorporating a pontoon member and a wheel. 33. The aircraft according to claim 32, wherein each propeller nacelle encloses a propeller shaft rotatably mounted therein, which propeller shaft protrudes from the aft end of die nacelle and past the aft edge of die wing on which the nacelle is located, each propeller shaft having a pusher propeller fixedly attached on the shaft at a point aft of the aft edge of die wing, said aircraft further comprising: two engines, tandemly mounted and opposed on the inside of die fuselage, each of said engines, when operating, causing rotation of an engine shaft, and belt drive means connecting each engine shaft to one or the other of the propeller shafts in such a manner that operation of the engines causes rotation of the two propellers. 34. The aircraft according to claim 33, wherein said engines are connected to a common gearbox which permits either engine to drive both propellers in die event of the shutdown of die otiier engine. 35. An aircraft comprising a fuselage and further comprising a forward landing gear component positioned forward of die center of gravity of the aircraft, substantially completely retractable into the fuselage, including integrated steerable ski and steerable wheel subcomponents; a main central landing gear component, substantially completely retractable into the fuselage, including integrated skis and steerable wheel subcomponents, each of which may be deployed to a point 8-13° aft of the center of gravity of the level aircraft and which, when retracted, assist in formation of a step in the fuselage at a point 8-13° aft of die center of gravity of the level aircraft; and a lateral stabilizing gear component comprising two bilaterally situated stabilizing members, each of which may be deployed on eitiier side of the aircraft to a point 8-13° aft of the center of gravity of the level aircraft and substantially aligned witii the main central landing gear, and each member including integrated pontoon and wheel subcomponents. 36. The aircraft according to claim 35, wherein each subcomponent of said forward landing gear component, said main central landing gear component, and said lateral stabilizing gear component, when fully deployed, is oriented at a point 10-11 ° aft of die center of gravity of the level aircraft.

Inventors: GEVERS DAVID E, GEVERS, DAVID, E.
Applicants: GEVERS DAVID E, GEVERS, DAVID, E.
Application year: 1994
Main classification: B64C25
IPC codes: B64C3, B64C25, B64C35, B64D27, B64D29, B64D35